Physical Layer Data Unit Format

ABSTRACT

In a wireless communication system wherein communication devices exchange information utilizing data units that conform to a first format, wherein the first format includes a short training field (STF) spread with a first spread code and a first cover code, a method is for generating a physical layer (PHY) data unit that conforms to a second format, wherein the PHY data unit is for transmitting PHY information. A first portion of the PHY data unit is generated to indicate the PHY data unit conforms to the second format, wherein the first portion of the PHY data unit includes an STF spread with at least one of a second spread code different than the first spread code or a second cover code different than the first cover code. A second portion of the PHY data unit is generated according to the second format, wherein the second portion of the PHY data unit includes PHY information elements not specified by the first format.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/100,948 filed Sep. 29, 2008, 61/101,833 filed Oct. 1,2008, 61/108,079 filed Oct. 24, 2008, and 61/120,973 filed Dec. 9, 2008,each of which is entitled “Control PHY Preamble Format for 60 GHzWideband Wireless Communication Systems.” This application also claimsthe benefit of U.S. Provisional Patent Application No. 61/110,357 filedOct. 31, 2008, 61/121,392 filed Dec. 10, 2008, 61/153,102 filed Feb. 17,2009, 61/171,343 filed Apr. 21, 2009, and 61/174,382 filed Apr. 30,2009, each of which is entitled “Control PHY for 60 GHz WidebandWireless Communication Systems.” This application also claims thebenefit of U.S. Provisional Patent Application No. 61/156,651 filed Mar.2, 2009, and entitled “Next Generation mmWave Specification.” Thedisclosures of all of the above-identified applications are herebyexpressly incorporated herein by reference.

FIELD OF TECHNOLOGY

The present disclosure relates generally to communication systems and,more particularly, to information formats for exchanging information viacommunication channels.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

An ever-increasing number of relatively inexpensive, low power wirelessdata communication services, networks and devices have been madeavailable over the past number of years, promising near wire speedtransmission and reliability. Various wireless technology is describedin detail in several IEEE standards documents, including for example,the IEEE Standard 802.11b (1999) and its updates and amendments, as wellas the IEEE 802.15.3 Draft Standard (2003) and the IEEE 802.15.3c DraftD0.0 Standard, all of which are collectively incorporated herein fullyby reference.

As one example, a type of a wireless network known as a wirelesspersonal area network (WPAN) involves the interconnection of devicesthat are typically, but not necessarily, physically located closertogether than wireless local area networks (WLANs) such as WLANs thatconform to the IEEE Standard 802.11a. Recently, the interest and demandfor particularly high data rates (e.g., in excess of 1 Gbps) in suchnetworks has significantly increased. One approach to realizing highdata rates in a WPAN is to use hundreds of MHz, or even several GHz, ofbandwidth. For example, the unlicensed 60 GHz band provides one suchpossible range of operation.

In general, transmission systems compliant with the IEEE 802.15.3c orfuture IEEE 802.11ad standards support one or both of a Single Carrier(SC) mode of operation and an Orthogonal Frequency Division Multiplexing(OFDM) mode of operation to achieve higher data transmission rates. Forexample, a simple, low-power handheld device may operate only in the SCmode, a more complex device that supports a longer range of operationmay operate only in the OFDM mode, and some dual-mode devices may switchbetween SC and OFDM modes. Additionally, devices operating in suchsystems may support a control mode of operation at the physical layer ofthe protocol stack, referred to herein as “control PHY.” Generallyspeaking, control PHY of a transmission system corresponds to the lowestdata rate supported by each of the devices operating in the transmissionsystem. Devices may transmit and receive control PHY frames tocommunicate basic control information such as beacon data or beamformingdata, for example.

The IEEE 802.15.3c Draft D0.0 Standard is directed to wireless widebandcommunication systems that operate in the 60 GHz band. In general,antennas and, accordingly, associated effective wireless channels arehighly directional at frequencies near or above 60 GHz. When multipleantennas are available at a transmitter, a receiver, or both, it istherefore important to apply efficient beam patterns to the antennas tobetter exploit spatial selectivity of the corresponding wirelesschannel. Generally speaking, beamforming or beamsteering creates aspatial gain pattern having one or more high gain lobes or beams (ascompared to the gain obtained by an omni-directional antenna) in one ormore particular directions, with reduced the gain in other directions.If the gain pattern for multiple transmit antennas, for example, isconfigured to produce a high gain lobe in the direction of a receiver,better transmission reliability can be obtained over that obtained withan omni-directional transmission.

Beamforming generally involves controlling the phase and/or amplitude ofa signal at each of a plurality of antennas to define a radiation orgain pattern. The set of amplitudes/phases applied to a plurality ofantennas to perform beamforming is often referred to as a steeringvector (or “phasor”). The IEEE 802.15.3c Draft D0.0 Standard proposes amethod for selecting a steering vector. For selecting a transmitsteering vector, the proposed method generally involves, for example,transmitting training signals during a training period using each of aplurality of steering vectors, determining the quality of the receivedtraining signals, and selecting a steering vector that corresponds tothe “best” received training signal.

SUMMARY

In one embodiment, in a wireless communication system whereincommunication devices exchange information utilizing data units thatconform to a first format, wherein the first format includes a shorttraining field (STF) spread with a first spread code and a first covercode, a method is for generating a physical layer (PHY) data unit thatconforms to a second format, wherein the PHY data unit is fortransmitting PHY information. The method comprises generating a firstportion of the PHY data unit to indicate the PHY data unit conforms tothe second format, wherein the first portion of the PHY data unitincludes an STF spread with at least one of a second spread codedifferent than the first spread code or a second cover code differentthan the first cover code. The method also comprises generating a secondportion of the PHY data unit according to the second format, wherein thesecond portion of the PHY data unit includes PHY information elementsnot specified by the first format.

In other embodiments, the method may comprise one or more (or none) ofthe following elements. The second spread code may be a complementarysequence of the first spread code, and wherein the first portion of thePHY data unit includes the STF spread with the second spread code. Thefirst spread code and the second spread code may be complimentary Golaysequences a and b, respectively. The STF of the first format maycomprise a plurality of consecutive Golay sequences a, and the STF ofthe second format may comprise a plurality of consecutive Golaysequences b. The STF of the second format may comprise a delimiter fieldafter the plurality of consecutive Golay sequences b, and the delimiterfield may include at least one Golay sequence −b. A Golay sequence a maybe included between the STF of the second format and a channelestimation field (CEF). The Golay sequence a between the STF of thesecond format and the CEF may serve as a cyclic prefix to a sequence inthe CEF.

In another embodiment, a communication device is for use in a wirelesscommunication system, wherein the communication device exchangesinformation with other communication devices utilizing data units thatconform to a first format, wherein the first format includes a shorttraining field (STF) spread with a first spread code and a first covercode, and utilizing a physical layer (PHY) data unit that conforms to asecond format, wherein the PHY data unit is for transmitting PHYinformation. The communication device comprises a PHY data unitgenerator configured to: generate a first portion of the PHY data unitto indicate the PHY data unit conforms to the second format, wherein thefirst portion of the PHY data unit includes an STF spread with at leastone of a second spread code different than the first spread code or asecond cover code different than the first cover code, and generate asecond portion of the PHY data unit according to the second format,wherein the second portion of the PHY data unit includes PHY informationelements not specified by the first format.

In other embodiments, the communication device may include one or more(or none) of the following elements. The second spread code may be acomplementary sequence of the first spread code, and the PHY data unitgenerator may be configured to generate the STF of the PHY data unitspread with the second spread code. The first spread code and the secondspread code may be complimentary Golay sequences a and b, respectively.The STF of the first format may comprise a plurality of consecutiveGolay sequences a, and the PHY data unit generator may be configured togenerate the STF of the PHY data unit to include a plurality ofconsecutive Golay sequences b. The PHY data unit generator may beconfigured to generate the STF of the PHY data unit to include adelimiter field after the plurality of consecutive Golay sequences b,and wherein delimiter field includes at least one Golay sequence −b. ThePHY data unit generator may be configured to include a Golay sequence abetween the STF of the second format and a channel estimation field(CEF).

In yet another embodiment, in a wireless communication system whereincommunication devices exchange information utilizing data units thatconform to a first format, wherein the first format includes a shorttraining field (STF) spread with a first spread code and a first covercode, a method is for generating processing a physical layer (PHY) dataunit that conforms to a second format, wherein the PHY data unit is fortransmitting PHY information. The method includes analyzing a firstportion of a received data unit to determine if the received data unitis a PHY data unit, wherein the first portion of the received data unitincludes an STF. Analyzing the first portion of a received data unit todetermine if the received data unit is a PHY data unit comprisesdetermining at least one of 1) whether the STF of the received data unitis spread with a second spread code different than the first spread codeor 2) whether the STF of the received data unit is spread with a secondcover code different than the first cover code. The method furtherincludes utilizing PHY information elements in a second portion of thePHY data unit to perform a PHY function if the received data unit is aPHY data unit, wherein the second portion of the PHY data unit conformsto the second format, and wherein the PHY information elements are notspecified by the first format.

In other embodiments, the method may include one or more (or none) ofthe following elements. The second spread code may be a complementarysequence of the first spread code, and analyzing the first portion ofthe received data unit may include determining whether the STF of thereceived data unit is spread with the second spread code. The firstspread code and the second spread code may be complimentary Golaysequences a and b, respectively. The STF of the first format may includea plurality of consecutive Golay sequences a, and wherein analyzing thefirst portion of the received data unit may include determining whetherthe STF of the received data unit comprises a plurality of consecutiveGolay sequences b. The STF of the second format may include a delimiterfield after the plurality of consecutive Golay sequences b, and whereindelimiter field includes at least one Golay sequence −b. The method mayfurther include detecting the delimiter field. A Golay sequence a may beincluded between the STF of the second format and a channel estimationfield (CEF).

In still another embodiment, a communication device is for use in awireless communication system, wherein the communication deviceexchanges information with other communication devices utilizing dataunits that conform to a first format, wherein the first format includesa short training field (STF) spread with a first spread code and a firstcover code, and utilizing a physical layer (PHY) data unit that conformsto a second format, wherein the PHY data unit is for transmitting PHYinformation. The communication device comprises a PHY data unit detectorconfigured to analyzing a first portion of a received data unit todetermine if the received data unit is a PHY data unit, wherein thefirst portion of the received data unit includes an STF. The PHY dataunit detector is also configured to determine if the received data unitis a PHY data unit based on determining at least one of 1) whether theSTF of the received data unit is spread with a second spread codedifferent than the first spread code or 2) whether the STF of thereceived data unit is spread with a second cover code different than thefirst cover code. The communication device further comprises a PHYcontroller to utilize the PHY information elements in a second portionof the PHY data unit to perform a PHY function if the received data unitis a PHY data unit. The second portion of the PHY data unit conforms tothe second format, and the PHY information elements are not specified bythe first format.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a communication system including atransmitter and a receiver that may communicate physical layer (PHY)information using data units that conform to a PHY data unit format;

FIG. 2 depicts block diagrams of a transmitter and a receiver that mayoperate in the system of in FIG. 1;

FIGS. 3A and 3B is a diagram of a prior art data unit format;

FIG. 4 is a diagram of a prior art superframe format;

FIG. 5 is a diagram of an example control physical layer (PHY) data unitformat;

FIG. 6 is a diagram of an example control PHY data unit format;

FIG. 7A is a diagram of spreading for a preamble of a default data unitformat;

FIG. 7B is a diagram of example spreading for a preamble of a controlPHY data unit format, wherein a complementary spreading sequence is usedcompared to the spreading of FIG. 7A;

FIG. 7C is a diagram of example spreading for a preamble of a controlPHY data unit format, wherein a different cover code is used compared tothe spreading of FIG. 7A;

FIGS. 8A and 8B are diagrams of an example format for a preamble of adefault data unit for a single carrier (SC) mode and an OrthogonalFrequency Division Multiplexing (OFDM) mode;

FIGS. 9A and 9B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a complementary spreading sequence isused in the STF compared to the format of FIGS. 8A and 8B;

FIGS. 10A and 10B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a different cover code is used in the STFcompared to the format of FIGS. 8A and 8B;

FIGS. 11A and 11B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a complementary spreading sequence isused in the STF compared to the format of FIGS. 8A and 8B;

FIGS. 12A and 12B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a different cover code is used in the STFcompared to the spreading of FIGS. 8A and 8B;

FIGS. 13A and 13B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a complementary spreading sequence isused in the STF compared to the format of FIGS. 8A and 8B;

FIGS. 13C and 13D are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a delimiter field is added in the STFprior to the CEF as compared to the format of FIGS. 8A and 8B;

FIGS. 13E and 13F are diagrams of further example formats for a preambleof a control PHY data unit, wherein a delimiter field is added in theSTF prior to the CEF as compared to the format of FIGS. 8A and 8B;

FIG. 14 is diagram of another example format for a preamble of a controlPHY data unit, wherein a complementary spreading sequence is used in theSTF compared to the spreading of FIGS. 8A and 8B;

FIG. 15 is diagram of another example format for a preamble of a controlPHY data unit, wherein a complementary spreading sequence is used in theSTF compared to the format of FIGS. 8A and 8B;

FIG. 16 is diagram of another example format for a preamble of a controlPHY data unit format, wherein a complementary spreading sequence is usedin the STF compared to the format of FIGS. 8A and 8B;

FIG. 17 is diagram of another example format for a preamble of a controlPHY data unit format, wherein a different cover code is used in the STFcompared to the format of FIGS. 8A and 8B;

FIG. 18 is diagram of another example format for a preamble of a controlPHY data unit format, wherein a complementary spreading sequence is usedin the STF compared to the format of FIGS. 8A and 8B;

FIG. 19 is diagram of another example format for a preamble of a controlPHY data unit format, wherein a complementary spreading sequence is usedin the STF compared to the format of FIGS. 8A and 8B;

FIG. 20 is diagram of another example format for a preamble of a controlPHY data unit format, wherein a complementary spreading sequence is usedin the STF compared to the format of FIGS. 8A and 8B;

FIG. 21 is diagram of an example correlator that me be used fordetecting an STF spread as in FIGS. 19 and 20;

FIG. 22 is diagram of an example correlator that utilize the correlatorof FIG. 21;

FIG. 23 is a block diagram of an example control PHY preamble generator;

FIG. 24 is a flow diagram of an example method for generating a controlPHY packet;

FIG. 25 is a flow diagram of an example method for detecting andutilizing a received control PHY packet;

FIG. 26 depicts an example architecture of a modulator of a transmitterthat may operate in the system of FIG. 1;

FIG. 27A is a block diagram of a correlator for correlating a signalwith Golay sequences;

FIG. 27B is a block diagram of a correlator for correlating a signalwith shorter sequences as compared to the correlator of FIG. 27A;

FIG. 27C is a block diagram of another correlator for correlating asignal with shorter sequences as compared to the correlator of FIG. 27A;

FIG. 28 is a block diagram of an example modulator and spreader for useby a transmitter that may operate in the system of FIG. 1;

FIGS. 29A and 29B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a different spreading sequence is used inthe STF as compared to the format of FIGS. 8A and 8B;

FIGS. 30A and 30B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a cyclic prefix in the STF is omitted ascompared to the formats of FIGS. 29A and 29B;

FIGS. 31A and 31B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein different spreading sequences are used inthe STF and in the CEF as compared to the format of FIGS. 8A and 8B;

FIGS. 32A and 32B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a cyclic prefix in the STF is omitted ascompared to the formats of FIGS. 31A and 31B;

FIGS. 33A and 33B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a spreading sequence of a differentlength is used in the STF as compared to the format of FIGS. 8A and 8B;

FIGS. 34A and 34B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein a cyclic prefix in the STF is omitted ascompared to the formats of FIGS. 33A and 33B;

FIGS. 35A are 35B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein an SFD field indicates whether the dataunit is related to beamforming;

FIGS. 36A are 36B are diagrams of example formats for a preamble of acontrol PHY data unit, wherein the ordering of channel estimationsequences in the CEF field indicates whether the control PHY data unitis related to beamforming;

FIGS. 37A-B and 38A-B are diagrams of example formats for a preamble ofa control PHY data unit, wherein an additional field between the STF andthe CEF is used to permit the use of identical channel estimationsequences in SC/OFDM default data units and control PHY data units; and

FIG. 39 are block diagrams of an example transmitter and an examplereceiver that may operate in the system of in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an example wireless communication system 10in which devices, such as a transmitting device 12 and a receivingdevice 14, may transmit and receive data units (e.g., packets) via ashared wireless communication channel 16. The devices 12 and 14 maycommunicate according to a communication protocol that utilizesdifferent physical layer (PHY)/media access control (MAC) layer packetformats depending on the mode of operation. For example, when thedevices 12 and 14 need to exchange information provided in a layer in aprotocol stack at or above the MAC layer, a first format is utilized,whereas if a control procedure such as beamforming training is beingperformed, a second format (“control PHY” format) is utilized. Ifdesired, control PHY may be associated with multiple sub-formats definedfor separate procedures (e.g., beacon transmission, beamforming),different network types (e.g., SC only, OFDM only, SC/OFDM), and/orother purposes. Each of the devices 12 and 14 may be, for example, amobile station or a non-mobile station equipped with a set of one ormore antennas 20-24 and 30-34, respectively. Although the wirelesscommunication system 10 illustrated in FIG. 1 includes two devices 12,14, each with three antennas, the wireless communication system 10 may,of course, include any number of devices, each equipped with the same ora different number of antennas (e.g., 1, 2, 3, 4 antennas and so on).For beamforming, however, at least one of the devices 12, 14 generallyshould include more than one antenna.

Also, it will be noted that although the wireless communication system10 illustrated in FIG. 1 includes a transmitting device 12 and areceiving device 14, devices in the wireless communication system 10 maygenerally operate in multiple modes (e.g., a transmit mode and a receivemode). Accordingly, in some embodiments, antennas 20-24 and 30-34 maysupport both transmission and reception. Alternatively or additionally,a given device may include separate transmit antennas and separatereceive antennas. It will be also understood that because each of thedevices 12 and 14 may have a single antenna or multiple antennas, thewireless communication system 10 may be a multiple input, multipleoutput (MIMO) system, a multiple input, single output (MISO) system, asingle input, multiple output (SIMO) system, or a single input, singleoutput (SISO) system. For beamforming, however, at least one of thedevices 12, 14 generally should include more than one antenna. Thus, inbeamforming, the system 10 will generally be a MIMO, MISO, or SIMOsystem.

In general, the communication system 10 may include SC-only, OFDM-only,or dual-mode (SC and OFDM) devices. To enable any device operating inthe communication system 10 to transmit and receive at least control PHYpackets, modulation of control PHY is preferably selected to match theslowest data rate (i.e., SC) supported in the communication system 10.In other words, because each OFDM device typically is capable ofprocessing at least control PHY packets associated with an SC mode,modulating control PHY packets using an SC mode generally provides anydevice with access to control PHY messaging. In other embodiments, eachdevice operating in the communication system 10 is an OFDM device, andmodulation of control PHY may be selected to match an OFDM modulationscheme, if desired. In yet other embodiments, the communication system10 includes only SC devices, and control PHY modulation is accordinglylimited to an SC mode only.

Although devices in the communication system 10 may transmit and receivecontrol PHY packets during various control procedures, the techniquesfor generating and receiving control PHY packets are discussed belowwith reference to beamforming. It will be noted, however, thatbeamforming packets may correspond to only one of a plurality of typesof the control PHY data units of the communication system 10. Areceiving device may accordingly determine, in the first instance,whether a packet is a control PHY packet, followed by determiningwhether the packet is a beamforming training (BFT) packet. In otherembodiments, control PHY format may be used exclusively for beamforming,while yet other embodiments may not include a separate PHY or MAC formatfor beamforming at all, and use the control PHY format for controlprocedures unrelated to beamforming. In some embodiments, there may be asingle control PHY format used for multiple purposes such as beamformingtraining, beacon transmission, etc. In other embodiments, separatecontrol PHY sub-formats may correspond to different purposes such asbeamforming beamforming training, beacon transmission, etc.

FIG. 2 illustrates, in relevant part, the architectures of thetransmitting device 12 and the receiving device 14. The transmittingdevice 12 may generally convert a sequence of information bits intosignals appropriate for transmission through a wireless channel (e.g.,channel 16 of FIG. 1). More specifically, the transmitting device 12 mayinclude an encoder 52 (e.g., a convolution encoder) that encodesinformation bits, a spreader 54 that converts each encoded bit to asequence of chips, and a modulator 56 that modulates the encoded chipsinto data symbols, which are mapped and converted to signals appropriatefor transmission via one or more transmit antennas 20-24. In general,the modulator 56 may implement any desired modulation techniques basedon one or more of phase shift keying, binary phase-shift keying (BPSK),π/2 BPSK (in which modulation is rotated by π/2 for each symbol or chipso that the maximum phase shift between adjacent symbols/chips isreduced from 180° to 90°), quadrature phase-shift keying (QPSK), π/2QPSK, frequency modulation, amplitude modulation, quadrature amplitudemodulation (QAM), π/2 QAM, on-off keying, minimum-shift keying, Gaussianminimum-shift keying, dual alternative mark inversion (DAMI), etc Insome embodiments, the modulator 56 may include a bit-to-symbol mapper 70that maps encoded bits into symbols, and a symbol-to-stream mapper 72that maps the symbols into multiple parallel streams. If only onetransmit antenna is utilized, the symbol-to-stream mapper 72 may beomitted. Information is transmitted in data units such as packets.

The transmitter 12 includes a control PHY controller 74 that generallycontrols operation when control PHY data units are transmitted and/orreceived. The control PHY controller 74 may include a BFT controller(not shown) that controls operation during a BFT period in which thetransmitter 12 cooperates with the receiver 14 to determine abeamforming vector or vectors for the transmitter 12 and/or the receiver14. The transmitter 12 also includes a control PHY packet generator 76that generates control PHY. For example, packets transmitted during aBFT period (which may be a type of control PHY packet) may have adifferent format as compared to non-control PHY packets, i.e., “regular”SC or OFDM packets used to convey information at or above the MAC layer.Regular packets, as opposed to control PHY packets, are referred toherein as “default packets” or packets that conforming to a “defaultformat.” In some embodiments, BFT packets may be different both fromregular packets and from control PHY packets not associated withbeamforming. For example, BFT packets may have a format that is asub-format of control PHY packets. The control PHY packet generator 76may be coupled to the control PHY controller 74 and may receive controlsignals from the control PHY controller 74. The control PHY packetgenerator 76 also may be coupled to the spreader 54 and/or the modulator56, and may cause the spreader 54 and/or the modulator 56 to operatedifferently when transmitting control PHY packets.

The transmitting device 12 may include various additional modules that,for purposes of clarity and conciseness, are not illustrated in FIG. 2.For example, the transmitting device 12 may include an interleaver thatinterleaves the encoded bits to mitigate burst errors. The transmittingdevice 12 may further include a radio frequency (RF) front end forperforming frequency upconversion, various filters, power amplifiers,and so on. Still further, while FIG. 2 illustrates a control PHYcontroller 74 a control PHY packet generator 76 dedicated specificallyto controlling during transmission/reception of control PHY packets andgenerating control PHY packets, the transmitting device 12 may alsoinclude one or several controllers associated with respective controlPHY procedures (such as BFT, beacon transmission, etc.) communicativelycoupled to a control PHY packet generator. For example, a transmittingdevice similar to the transmitting device 12 may include a control PHYpacket generator that generates packets according to one control PHYformat or multiple control PHY sub-formats (including a beamformingformat, if desired), and a control PHY controller that controls variouscontrol PHY procedures (optionally including beamforming). In thisembodiment, the control PHY packet generator and the control PHYcontroller may be coupled to other components of the correspondingtransmitting device in a manner.

The receiving device 14 may include a pre-processor for space-time codesand equalizer 84 coupled to one or more receive antennas 30-34, ademodulator 86, a despreader 88, and a decoder 90. If only one receiveantenna is utilized, the pre-processor for space-time codes may beomitted, and the unit 84 may include an equalizer. The receiving device14 also includes a control PHY packet detector 92 and a control PHYcontroller 94 that generally controls operation during reception and/ortransmission of control PHY packets. For example, the control PHYcontroller 94 may include a BFT controller (not shown) that controlsoperation during a BFT period in which the receiver 14 cooperates withthe transmitter 12 to determine a beamforming vector or vectors for thetransmitter 12 and/or the receiver 14. The control PHY packet detector92 generally detects control PHY packets and, when detected, causes thecontrol PHY packets to be forwarded to the control PHY controller 94. Itwill be understood that the receiving device 14 may also include othercomponents such as filters, analog-to-digital converters, etc. that areomitted from FIG. 2 for the purposes of clarity and conciseness.

Similar to the transmitting device 12, the receiving device 14 mayinclude components for processing control PHY packets in addition to, orin instead of, the control PHY packet detector 92 and a control PHYcontroller 94. In an embodiment, a control PHY packet detector may becoupled to a BFT controller, a beacon controller, and other componentsassociated with respective control PHY procedures, or the control PHYcontroller may include the BFT controller, the beacon controller, etc.

As will be described in more detail below, a control PHY packet may besignaled by modified spreading of a preamble and/or a header of apacket. Thus, in these embodiments, the control PHY packet detector 92may analyze the spreading of the preamble and/or the header of a packet.In these embodiments, the control PHY packet detector 92 may be coupledto the despreader 88.

As discussed above, the transmitting device 12 may also operate in areceive mode, and the receiving device 14 may also operate in a transmitmode. Thus, the transmitting device 12 may include at least some of thesame or similar components as the receiving device 14, and vice versa.

In general, the devices 12 and 14 may communicate using a packet formatthat allows for shorter packets, for example, as compared to a formatutilized, for example, to communicate information originating fromlayers at or above the MAC layer. For example, much information conveyedin a PHY header and/or a MAC header may be un-needed for some controlPHY functions. Thus, the present disclosure provides various embodimentsof a control PHY data unit format that omits or reinterprets fields inthe data unit (e.g., in the PHY header and/or the MAC header) so that,in some implementations or for some control PHY data units, the dataunit length may be shortened and/or filled with more control PHYinformation as compared to packets utilized, for example, to communicateinformation originating from layers at or above the MAC layer. Thecontrol PHY packet generator 76 may generate the control PHY packets.For example, the control PHY packet generator 76 may generate thecontrol PHY packets during the BFT period.

The present disclosure further provides several embodiments of a controlPHY format that devices in the communication system 10 may utilize forcontrol procedures other than beamforming, or both for beamforming andother control procedures. According to another aspect of the presentdisclosure, at least some of the embodiments of control PHY formatenable the receiving device 14 to detect a control PHY packet relativelyearly, i.e., prior to receiving the entire data unit, prior to receivingthe entire data unit header, or even prior to receiving the entire PHYheader. As discussed in more detail below, some of these embodimentsallow control PHY detection based only on a portion of the shorttraining field (STF) of the packet preamble, some embodiments involveprocessing the STF and at least a portion of the channel estimationfield (CEF), still other embodiments involve processing the STF and anintermediate field preceding the CEF (such as a delimiter field), etc.Early control PHY detection in turn allows the receiving device 14 toadjust synchronization algorithms and determine whether, for example,the header and/or the payload of the packet will require decoding. Asone example, the receiving device may use the results of early detectionto assess the length of one or several fields in the preamble becausethe STF of a control PHY may include a significantly larger number oftraining sequences than the STF of a regular packet. As another example,an OFDM-only device may receive a packet modulated according to an SCmodulation scheme. Because this device may not be able to decode theheader and the payload of a regular SC packet, but nevertheless may beable to decode the header and the payload of a control PHY packet, earlydetection can eliminate certain unnecessary steps and reduce the numberprocessing errors at the OFDM-only device.

In time division multiple access (TDMA)-type networks (e.g. channel timeallocation (CTA) periods in the superframe structure described in theIEEE 802.15.3c Draft D0.0 Standard), beamforming often requirestransmitting training signals in frames (e.g., sounding packets) duringtime slots dedicated to BF training between the transmitter 12 and thereceiver 14. For example, if the transmitter 12 has multiple antennas,the transmitter 12 may transmit a plurality of sounding packets to thereceiver 14, where each sounding packet is sent using a differenttransmit beamforming vector. The receiver 14 may analyze the quality ofeach of the received sounding packets, and may transmit a feedbackpacket to the transmitter 12 indicating the “best” transmit beamformingvector. Similarly, if the receiver 14 has multiple antennas, thereceiver 14 may request that the transmitter 12 transmit a plurality ofsounding packets to the receiver 14. The receiver 14 may receive eachsounding packet using a different receive beamforming vector. Thereceiver 14 may then analyze the quality of each of the receivedsounding packets choose a “best” receive beamforming vector.

FIG. 3A is a diagram of a prior art physical layer packet format 120.For instance, the IEEE 802.15.3c Draft D0.0 Standard utilizes the packetformat 120. The packet 120 includes a preamble 122, a header 130, and apayload 132. In the IEEE 802.15.3c Draft D0.0 Standard, the preamble 122generally provides training information that helps the receiver 14detect the packet 120, adjust an automatic gain control (AGC) setting,obtain frequency and timing synchronization, etc. Also in the IEEE802.15.3c Draft D0.0 Standard, the header 130 provides information ofthe basic PHY parameters required for decoding the payload (e.g. alength of the payload, modulation/coding method, pilot insertioninformation, cyclic prefix length in OFDM mode, preamble length of thenext packet, reserved fields, etc.) so that the receiver 14 can adjustits decoding apparatus accordingly. The header 130 also includes MAClayer information.

FIG. 3B is a diagram illustrating a format of the header 130 specifiedin the IEEE 802.15.3c Draft D0.0 Standard. The header 130 includes a PHYheader 140, a MAC header 144 (including a header check sequence (HCS)),and Reed-Solomon parity bits 148 generated from the MAC header 144.Optionally, the header 130 may include a MAC subheader 152 (including anHCS) and Reed-Solomon parity bits 156 generated from the MAC subheader152.

As discussed above, the IEEE 802.15.3c Draft D0.0 Standard provides forTDMA-type communications. In a TDMA mode, each device is (or two devicesare) allocated a dedicated time slot by the network controller, so thatonly a particular device (or a particular pair of devices) is (are)communicating during the time slot, where the other devices will be setto idle to save power. The time slot may be set so that only one device(STA1) may transmit data to the other (STA2), and STA2 may only sendacknowledgment (ACK) or failure (NAK) to STA1 (often referred to as a“single direction” allocated time slot). The time slot may also be setso that both STA1 and STA2 can send data to each other (often referredto as a “bi-direction” allocated time slot).

An example of TDMA communications is seen in the super-frame structuredescribed in the IEEE 802.15.3c Draft D0.0 Standard. A superframe 170may include a beacon period 174, a contention access period (CAP) 178,and a channel time allocation (CTA) period 182. The beacon period 174generally is used for transmitting control information to a piconet,allocating guaranteed time slots (GTSs), synchronization, etc. The CAPperiod 178 generally is used for authentication/associationrequests/responses, channel time requests, etc. The CTA period 182 isgenerally used for providing single direction allocated time slots andbi-direction allocated time slots. The CTA period 182 may includemanagement CTA slots 186 and n CTA slots 190. Beamforming training (ormaybe other purposes like antenna switching, time-domain precoding,beacon transmission, etc) may be conducted in one or more CTA slots 190,for example. For BFT, for example, the BFT period may involvetransmitting BFT sounding packets over different directions (e.g., usingdifferent beamforming vectors), and a “best” direction may be chosen.During the BFT period, channel quality cannot be guaranteed. Thus, datatransmission may be delayed until after BFT is finished and abeamforming vector has been selected.

The CTA in which BFT is to take place may already be allocated to aparticular pair of devices (STA1 and STA2). Both STA1 and STA2 may havepre knowledge of the other's MAC address. Thus, providing source anddestination MAC addresses in a MAC header of a BFT sounding packetduring a CTA 190 may, in effect, be transmitting already knowninformation. Additionally, other information in the header of the packet120 (FIG. 3) may not be needed for BFT.

FIG. 5 is a block diagram of an embodiment of a new physical layer dataunit format 200 to be used in protocol functions such as beamformingtraining, antenna switching, time-domain precoding, beacon transmission,etc. The format 200 will typically be used for an exchange ofinformation for the physical layer (PHY), as opposed to exchanging dataunits that originated from the MAC layer or higher. For example, PHYprocesses in a pair of communication devices may need to exchangeinformation for purposes of, for example, beamforming training (BFT),antenna switching, time-domain precoding, beacon transmission, etc., andsuch information may be transmitted in data units that conform to theformat 200. On the other hand, another format (referred to herein as the“default format”), such as the format 120 of FIG. 3A, will be utilizedwhen communicating data units that originate from the MAC layer orhigher. Typically, data units conforming to the format 200 (i.e.,control PHY data units) will have a shorter length than data unitsconforming to the default format (i.e., default data units). The format200 may be used for BFT data units, i.e., data units sent during BFT. Itis to be understood, however, that the format 200 may be used for otherfunctions such as antenna switching, time-domain precoding, beacontransmission, etc. Also, as indicated above, the control PHY data unitformat 200 may correspond to only one of several control PHY data unitsub-formats.

The control PHY packet 200 includes a preamble 204 and a header 208. Afirst portion 212 of the control PHY packet 200 includes the preamble204 and may include a beginning portion of the header 208. The firstportion 212 is encoded to indicate that the packet conforms to thecontrol PHY packet format 200 as opposed to the default format (e.g.,the format 120 of FIG. 3A). The first portion 212 may be encoded in avariety of ways. For example, in some embodiments, the preamble 204and/or the PHY header may be encoded to indicate the control PHY packetformat 200 by utilizing different spreading sequences than the defaultformat. In some embodiments, only a section 214 of the first portion 212may be formatted differently than the respective portion of the preamble122. Although the section 214 is illustrated in FIG. 5 as being at thebeginning of the packet 200, the section 214 could be located, ingeneral, in any part of the first portion 212. In other words, not allof the first portion 212 need be formatted differently than the defaultformat. Preferably but not necessarily, the portion 214 in theseembodiments is in an earlier section of the preamble 204 (as measuredfrom the perspective of a receiving device) to allow earlyidentification of the control PHY packet format based only on theportion 214. In other embodiments, other information in the firstportion may indicate a sub-format of the control PHY packet. Forexample, a field in a PHY header portion of the header 208 may indicatethe control PHY packet is a BFT packet. In still other embodiments,combinations of modulation, spread codes, and PHY header fields may beused to indicate a control PHY packet and a sub-format of the controlPHY packet. Various embodiments of an encoded first portion 212 aredescribed in further detail below. If there are multiple types ofcontrol PHY packets, or sub-formats of a control PHY packet, a field inthe PHY header may indicate to which format the control PHY packetconforms. For example, a field in the PHY header may indicate whetherthe control PHY is a BFT packet. As another example, a field in the PHYheader may indicate whether the control PHY includes a payload.

Generally, the first portion 212 may conform to the default format atleast in some respects. On the other hand, a second portion 216 of thecontrol PHY packet 200 generally does not conform to the default format,but rather conforms to the format 200. For example, if a receiverdetermines that a received packet conforms to the format 200, thereceiver may reinterpret fields in the second portion 216 as compared tofields specified by the default format. For example, header fieldsspecified by the default format could be used for control PHY fields(e.g., BFT fields) not specified by the default format. For example, amodulation and coding scheme (MCS) field, a cyclic prefix (CP) lengthfield, reserved bits, etc., could be utilized for BFT information suchas one or more of a BFT countdown identifier (ID) number, a feedbackindication bit (e.g., if set to 1 it may indicate that a beamforming(BF) ID number field may be interpreted as an indicator of the “best” BFdirection), a receive BF sweeping request subfield (e.g., the stationperforming receive BF may request that a transmitter send a plurality ofBFT sounding packets, and the number of BFT sounding packets requestedis indicated; a zero indicates receive BFT is not requested), a fieldindicating a forward/reverse link direction, other subfields to be usedfor exchanging information elements used for channel sounding for BF,etc. In embodiments in which the format 200 is not for BFT, fieldsspecified in the default format could be utilized for antenna switchingtraining information, time-domain precoding information, MCS feedbackinformation, beacon transmission, etc. Thus, upon receiving a packetthat conforms to the format 200, a receiver may utilize information inthe packet to perform a PHY function such as selecting a beamformingvector, performing time-domain precoding, selecting an MCS, performingchannel estimation, beacon transmission, etc.

In some embodiments, the control PHY packet 200 may include a payload220, whereas in other embodiments the control PHY packet 200 may omitthe payload 220. In embodiments that include a payload 220, the format200 may permit the payload 220 to be selectively omitted. For instance,the first portion 212 or the second portion 216 may be encoded toindicate whether the data unit 200 includes the payload 220. In someembodiments, the control PHY packet 200 may omit the MAC header portionin the header 208 and may also omit the payload 220. In anotherembodiment, the control PHY packet 200 may extend after the PHY header320 and include at least a portion of a MAC header and/or a payload. Forexample, the control PHY packet 200 may include a MAC header, or only aportion of the MAC header, such as the MAC destination address. Inanother embodiment, the control PHY packet 200 may include a payload,but omit the MAC header. The payload may be used to transmit controlPHY-related IEs, for example. In one embodiment, the payload may have afixed length.

In one embodiment, a payload length field in the PHY header (included inthe header 208 and the first portion 212) may be set to zero to indicatethat the control PHY packet 200 is a BFT packet. If the payload lengthfield is set to zero, other header fields specified by the defaultformat could be used for BFT purposes (or antenna switching traininginformation, time-domain precoding information, MCS feedbackinformation, beacon transmission, etc.).

A control PHY packet may be signaled by modified spreading of a preambleand/or a header of a packet. An example packet format common to bothdefault packets and control PHY packets will now be described withreference to FIG. 6. A packet 550 may include a preamble 554, a header556, and optionally a payload 558 (e.g., the payload 558 may be omittedin control PHY packets). The preamble 554 generally provides traininginformation that helps a receiver to detect a current packet, adjust anAGC (Automatic Gain Control) setting, synchronize frequency and timing,etc. The header 556 generally includes information for basic (e.g., PHY)parameters for decoding the payload 558 (e.g. length of the payload,modulation/coding method, etc.) so that the receiver can adjust itsdecoding apparatus accordingly. The preamble 554 may include a shorttraining field (STF) 560 and a channel estimation field (CEF) 562. TheSTF 560 generally includes information that is useful forsynchronization, whereas the CEF 562 generally includes information thatis useful for channel estimation. For example, the STF 560 may include asynchronization (sync) sequence, and the CEF may include a channelestimation sequence (CES).

In some embodiments, the preamble 554 may have the same general formatin both default packets and control PHY packets, as will be described inmore detail below, except that spreading may be modified. In theseembodiments, the format of the header 556 may differ between defaultpackets and control PHY packets. For example, the header of a controlPHY packet may be longer than in a default packet. Similarly, thepayload 558 optionally may be omitted in at least some control PHYpackets.

In other embodiments, the preamble 554 may have a different format indefault packets as compared to control PHY packets, as will be describedin more detail below. For example, in some embodiments, the STF 560 maybe longer in control PHY packets as compared to default packets. Asanother example, the CEF 562 may be longer as compared to defaultpackets. As yet another example, the STF 560 may be longer and the CEF562 may be shorter in control PHY packets as compared to defaultpackets. As still another example, the STF 560 may be longer and the CEF562 may be omitted in at least some control PHY packets as compared todefault packets.

FIG. 7A is a diagram of an example STF 580 in a default packet. The STF580 includes a plurality of sequences a which may be Golay sequences(Ga). For example, the sequence a may be a length-128 sequence (or someother suitable length). FIG. 7B is a diagram of an example STF 584 in acontrol PHY packet that corresponds to the STF 580 of the defaultpacket. The STF 584 includes a plurality of sequences b which may beGolay sequences (Gb). The sequence b is a complementary sequence to theGolay sequence a. Generally, the two complementary sequences a and bhave correlation properties suitable for detection at a receivingdevice. For example, the complementary spreading sequences a and b maybe selected so that the sum of corresponding out-of-phase aperiodicautocorrelation coefficients of the sequences a and b is zero. In someembodiments, the complementary sequences a and b have a zero oralmost-zero periodic cross-correlation. In another aspect, the sequencesa and b may have aperiodic cross-correlation with a narrow main lobe andlow-level side lobes, or aperiodic auto-correlation with a narrow mainlobe and low-level side lobes.

In some embodiments, the number of sequences b in the STF 584 is greaterthan the number of sequences a in the STF 580. This may help withsynchronization in situations in which the signal to noise ratio (SNR)is lower in the transmission of control PHY packets as compared todefault operation.

FIG. 7C is a diagram of another example STF 588 in a control PHY packetthat corresponds to the STF 580 of the default packet. The STF 588includes a plurality of sequences a as in the STF 580. In the STF 588,however, the sign of alternate sequences a are flipped. In FIG. 7C, aminus sign may indicate that modulation is 180 degrees out of phase ascompared to a non-negative sequence. In some embodiments, the number ofsequences a in the STF 588 is greater than the number of sequences a inthe STF 580. This may help with synchronization in situations in whichthe signal to noise ratio (SNR) is lower in the transmission of controlPHY packets as compared to default operation.

In some embodiments, the CEF following the STF 584 and/or the STF 588may be the same length as the CEF following the STF 580. In otherembodiments, the CEF following the STF 584 and/or the STF 588 may belonger than the CEF following the STF 580. For example, if the length ofthe sequence a is L (e.g., L=128 or some other suitable length), thenthe length of the CEF following the STF 584 and/or the STF 588 may beK*L longer than the CEF following the STF 580, where K is an integergreater than or equal to one. In these embodiments, the additionallength in the CEF may be used for more reliable frame timing, and/or tokeep channel estimation sequences the same as in default packets.

In still other embodiments, the CEF following the STF 584 and/or the STF588 may be shorter than the CEF following the STF 580. For example, theCEF following the STF 584 and/or the STF 588 may be one half the lengthof the CEF following the STF 580, or some other suitable shorter length.In still other embodiments, the CEF may be omitted following the STF 584and/or the STF 588.

FIGS. 8A and 8B are diagrams of a preamble format for a default packetin a single carrier (SC) mode and an OFDM mode. In particular, FIG. 8Ais a diagram of the preamble format 600 for SC mode, and FIG. 8B is adiagram of the preamble format 604 for OFDM mode. In FIG. 8A, an STFcomprises a plurality of sequences a which may be Golay sequences (Ga).For example, the sequence a may be a length-128 sequence (or some othersuitable length). A CEF of the preamble 600 comprises a pattern of thesequence a, and a complementary sequence b, which may also be a Golaysequence (Gb) of the same length as the sequence a, where a and b may bemodified by a cover code. As used herein, the term “cover code” refersto how a series of sequences are augmented to form a longer sequence.For example, for a sequence [−b, +a, +b, +a], where a and b arecomplementary sequences, the cover code may be represented as [−1, +1,+1, +1], where −1 may indicate that the binary complement of the code aor b is utilized, or that the modulated signal corresponding to code −a,for example, is phase shifted by 180° with respect to the modulatedsignal corresponding to code +a. In this example [−b, +a, +b, +a], thecover code could be represented differently, such as [0, 1, 1, 1], wherethe first 0 indicates that −b is utilized. A plurality of a and bsequences in the CEF may form composite sequences u and v, where u and vare themselves complementary sequences. In some embodiments, u and v arethemselves complementary Golay sequences. If the sequences a and b areeach of length 128, then the sequences u and v are each of length 512. Asequence v_(s) is merely the sequence −b, and the sequence v_(s) acts asa cyclic postfix.

As can be seen in FIGS. 8A and 8B, the STF in both the SC mode and theOFDM mode is the same (i.e., a plurality of a sequences). Also, the CEFin both the SC mode and the OFDM mode is similar, except that the orderof the sequences u and v is reversed. Also, it can be seen that v_(s)acts as a cyclic postfix for both u and v.

If a communication protocol permits both SC and OFDM transmissions, acommon control PHY format in general may be defined for SCtransmissions, OFDM transmissions, or for both SC and OFDMtransmissions. For example, a common control PHY format may betransmitted using SC modulation for a protocol that permits both SC andOFDM transmissions. However, it is also possible to define separatecontrol PHY formats for SC transmissions and OFDM transmissions.

FIGS. 9A and 9B are diagrams of two example preamble formats for acontrol PHY packet, and that correspond to the default formatillustrated in FIGS. 8A and 8B. In particular, FIG. 9A is a diagram ofthe control PHY preamble format 608, which corresponds to FIG. 8A. FIG.9B is a diagram of the control PHY preamble format 612, whichcorresponds to FIG. 8B. In the formats illustrated in FIGS. 9A and 9B,the complementary sequence b is used in the STF to signal that thepacket is a control PHY packet. Also in the formats illustrated in FIGS.9A and 9B, the CEF is same length as in the formats of FIGS. 8A and 8B.It is noted, however, that the a and b sequences are swapped in theCEF's of FIGS. 9A and 9B as compared to the CEF's of FIGS. 8A and 8B,respectively, so that the preamble includes different sequences at theend of the STF field and at the start of the CEF field. In this manner,the preamble may efficiently signal the beginning of the CEF field.

FIGS. 10A and 10B are diagrams of a two example formats for a controlPHY packet, and that correspond to the default formats illustrated inFIGS. 8A and 8B. In particular, FIG. 10A is a diagram of the preambleformat 620, which corresponds to FIG. 8A. FIG. 10B is a diagram of thepreamble format 624, which corresponds to FIG. 8B. In the formatsillustrated in FIGS. 10A and 10B, the sign of alternate sequences in theSTF is flipped as compared to the STF in the default mode preamble tosignal that the packet is a control PHY packet. Also in the formatsillustrated in FIGS. 10A and 10B, the CEF is same length as in theformats of FIGS. 8A and 8B. It is also noted that the CEF's in FIGS. 9Aand 9B are the same as in FIGS. 8A and 8B, respectively.

FIGS. 11A and 11B are diagrams of two example preamble formats for acontrol PHY packet, and that correspond to the default formatsillustrated in FIGS. 8A and 8B. In particular, FIG. 11A is a diagram ofthe preamble format 630, which corresponds to FIG. 8A. FIG. 11B is adiagram of the preamble format 634, which corresponds to FIG. 8B. In theformats illustrated in FIGS. 11A and 11B, the complementary sequence bis used in the STF to signal that the packet is a control PHY packet.Also in the formats illustrated in FIGS. 11A and 11B, a delimiter field638 is included between the STF and the CEF. The delimiter field 638 maybe useful for improving frame timing reliability, for example. Thedelimiter field 638 may include one or more sequences a. It is notedthat the CEF's in FIGS. 11A and 11B are the same as in FIGS. 8A and 8B,respectively.

FIGS. 12A and 12B are diagrams of two example preamble formats for acontrol PHY packet, and that correspond to the default formatsillustrated in FIGS. 8A and 8B. In particular, FIG. 12A is a diagram ofthe preamble format 640, which corresponds to FIG. 8A. FIG. 12B is adiagram of the preamble format 644, which corresponds to FIG. 8B. In theformats illustrated in FIGS. 12A and 12B, the sign of alternatesequences in the STF is flipped as compared to the STF in the defaultmode preamble to signal that the packet is a control PHY packet. Also inthe formats illustrated in FIGS. 12A and 12B, a delimiter field 648 isincluded between the STF and the CEF. The delimiter field 648 may beuseful for improving frame timing reliability, for example. Thedelimiter field 648 may include one or more sequences b. Also in theformats illustrated in FIGS. 12A and 12B, the CEF is same length as inthe formats of FIGS. 8A and 8B. It is noted, however, that the a and bsequences are swapped in the CEF's of FIGS. 12A and 12B as compared tothe CEF's of FIGS. 8A and 8B, respectively.

FIGS. 13A and 13B are diagrams of two example preamble formats for acontrol PHY packet, and that correspond to the default formatsillustrated in FIGS. 8A and 8B. In particular, FIG. 13A is a diagram ofthe preamble format 650, which corresponds to FIG. 8A. FIG. 13B is adiagram of the preamble format 654, which corresponds to FIG. 8B. In theformats illustrated in FIGS. 13A and 13B, the complementary sequence bis used in the STF to signal that the packet is a control PHY packet.Also in the formats illustrated in FIGS. 13A and 13B, a delimiter field658 is included between the STF and the CEF. The delimiter field 658 maybe useful for improving frame timing reliability, for example. Thedelimiter field 658 may include one or more sequences −b. Also in theformats illustrated in FIGS. 13A and 13B, the CEF is same length as inthe formats of FIGS. 8A and 8B. It is noted, however, that the a and bsequences are swapped in the CEF's of FIGS. 13A and 13B as compared tothe CEF's of FIGS. 8A and 8B, respectively.

FIGS. 13C and 13D are diagrams of two example preamble formats for acontrol PHY packet. In the preamble formats 655 and 657, the samecomplementary sequence a is used in the STF as in the default formatsillustrated in FIGS. 8A and 8B, respectively, and a delimiter field 656between the STF and the CEF signals that the packet is a control PHYpacket. The delimiter field 656 may include one or more sequences b. Ascompared to the formats of FIGS. 8A and 8B, the a and b sequences areswapped in the CEF's of FIGS. 13C and 13D, respectively.

Next, FIGS. 13E and 13F depict two example preamble formats for acontrol PHY packet in which the sequence a is used in the STF of thepreamble format 659 and the preamble format 661. The control PHY formats695 and 661 correspond to the default formats in FIGS. 8A and 8B,respectively. Similar to the formats illustrated in FIGS. 13C and 13D,the formats 659 and 661 utilize the same sequence in the STF as therespective formats of FIGS. 8A and 8B. The delimiter field 660 includesone or more sequences −a to signal, by flipping the sign of the sequencea relative to the preceding STF field, that the packet is a control PHYpacket. To ensure efficient detection and correlation of the CEFsequences in the CEF, the signs of a and b sequences are flipped in theCEF's of FIGS. 13E and 13F as compared to the CEF's of FIGS. 8A and 8B,respectively.

Referring now to the examples of FIGS. 11A, 11B, 12A, 12B, and 13A-13F,in an alternative, the CEF may be omitted.

Referring now to the examples of FIGS. 9A, 9B, 10A, 10B, 11A, 11B, 12A,12B, 13A-13F, in an alternative, the CEF may be of approximately halfthe length as in the preamble of a default packet. FIG. 14 is an exampleformat 666 for a preamble for a control PHY packet in which the controlPHY packet is signaled by using the complementary sequence b in the STF.The format 666 also includes a delimiter field 668 having one or more −bsequences. Further, the format 660 includes a CEF that includes only onecomposite sequence u (as opposed to two composite, complementarysequences u and v). The CEF includes a cyclic postfix field u_(s), whichis optional and may be omitted in some implementations. FIG. 15 isanother example format 670 for a preamble for a control PHY packet inwhich the control PHY packet is signaled by using the complementarysequence b in the STF. The format 670 includes a CEF that includes onlyone composite sequence u (as opposed to two composite, complementarysequences u and v). A first sequence of u (−b) is phase shifted by 180degrees with respect to the sequences used in the STF. The particular usequences shown in FIGS. 14 and 15 are not required. Rather, anysuitable u (e.g., a Golay sequence) composed of a and b complementarysequences may be utilized. For instance, if there is no delimiter field,u may be selected so that it begins with a complementary sequence to thelast sequence in STF.

Referring now to the examples of FIGS. 9A, 9B, 10A, 10B, 11A, 11B, 12A,12B, 13A-13F, in an alternative, the CEF may be approximately multipletimes (e.g., 2 or more) the length as in the preamble of a defaultpacket. FIG. 16 is a diagram of an example format 680 for a preamble fora control PHY packet in which the control PHY packet is signaled byusing the complementary sequence b in the STF. The format 680 is similarto the format 608 of FIG. 9A except that the CEF in the format 680includes two or more u sequences and two or more v sequences. FIG. 17 isa diagram of an example format 690 for a preamble for a control PHYpacket in which the control PHY packet is signaled by using thealternating +a, −a sequences in the STF. The format 690 is similar tothe format 620 of FIG. 10A except that the CEF in the format 690includes two or more u sequences and two or more v sequences. FIG. 18 isa diagram of an example format 700 for a preamble for a control PHYpacket in which the control PHY packet is signaled by using thecomplementary sequence b in the STF. The format 700 includes a delimiterfield 704 having one or more sequences −b. The CEF includes two or moreu sequences and two or more v sequences. The receiver of a data unitthat conforms to the formats 680, 690, or 700 may perform channelestimation two or more times using the repetitions of u and v sequences.The receiver may then average the results, for example, to improve theoverall quality of channel estimation.

In the examples of FIGS. 16-18, as with the examples of FIGS. 9A, 9B,10A, 10B, 11A, 11B, 12A, 12B, 13A-13F, the last sequence of the STF(when no delimiter field) or the last sequence of the delimiter field(when included) may act as a cyclic prefix of the first composite symbolin the CEF. Also, in the examples of FIGS. 16-18, as with the examplesof FIGS. 9A, 9B, 10A, 10B, 11A, 11B, 12A, 12B, 12A, and 12B, the lastsequence of the composite sequence u may act as a cyclic prefix of v,and vice versa. Similarly, the first sequence of the composite sequencev may act as a cyclic postfix of u, and vice versa. When multiplesequences u and v are included in the CEF, the receiver may generate achannel estimation for each u, v pair, and then combine the results byaveraging, for example.

Referring again to FIG. 2, with default formats as discussed withreference to FIGS. 8A and 8B and control PHY preamble formats asdiscussed with reference to FIGS. 9A, 9B, 10A, 10B, 13A, 13B, 14 and 15,the control PHY detector 92 may include a correlator configured to crosscorrelate with the sequence a (an “a correlator”) and a correlatorconfigured to cross correlate with the sequence b (a “b correlator”), inone embodiment. In this embodiment, the control PHY detector 92 mayutilize the output of the a correlator and the output of the bcorrelator to determine when an SFD of a default packet or an SFD of acontrol PHY packet has been received. With control PHY preamble formatsas discussed with reference to FIGS. 10A, 10B, 12A and 12B, the controlPHY detector 92 may include an a correlator and a correlator configuredto cross correlate with the sequence −a (a “−a correlator”), in oneembodiment. In this embodiment, the control PHY detector 92 may utilizethe output of the a correlator and the output of the −a correlator todetermine when an STF of a default packet or an STF of a control PHYpacket has been received. In another embodiment for use with preambleformats as discussed with reference to FIGS. 10A, 10B, 12A and 12B, thecontrol PHY detector 92 may include an a correlator and may utilize theoutput of the a correlator to determine when an STF of a default packetor an STF of a control PHY packet has been received.

In other embodiments, a control PHY packet may be signaled usingrepeated sequences in the STF that are double the length of a. Forexample, if a is a length-128 sequence, a control PHY packet may besignaled using repeated length-256 sequences in the STF. The length ofSTF may be the same as in the default mode. In other words, the numberof double-length sequences may be one half the number of a sequences inthe STF of the default packet. In one embodiment, the double-lengthsequences are combinations of the complementary sequences a and b. Inthis embodiment, and if the CEF also utilizes the sequences a and b, ana correlator and a b correlator may be reused for both control PHYpacket detection and channel estimation in default mode.

A double-length sequence m may be utilized in the STF to signal acontrol PHY packet. The sequence m may be any of the followingcombinations of the complementary sequences a and b: [b a], [b −a], [ab], or [a −b]. If the sequences a and b are Golay sequences (Ga, Gb),then a double-length Golay sequence Gm may be used, and Gm may be any ofthe following: [Gb Ga], [Gb −Ga], [Ga Gb], or [Ga −Gb].

If a delimiter field is utilized, the delimiter field may utilize one ormore of the following double-length sequences: −m or n, where n is acomplementary sequence of m. For example, if m is [b a], [b −a], [a b],or [a −b], then n may be [b −a], [b a], [a −b], or [a b], respectively.If the sequences a and b are Golay sequences (Ga, Gb), and if Gm is [GbGa], [Gb −Ga], [Ga Gb], or [Ga −Gb], then n may be a Golay sequence (Gn)and may be [Gb −Ga], [Gb Ga], [Ga −Gb], or [Ga Gb], respectively. Inthese embodiments in which double-length sequences are utilized in theSTF, composite sequences for the CEF may be selected so that the lasthalf-length sequence of the STF (when no delimiter field) or the lasthalf-length sequence of the delimiter field (when included) may act as acyclic prefix of the first composite sequence in the CEF. For example,if the a sequence is a length-128 sequence, the last 128 chips of theSTF (when no delimiter field) or the last 128 chips of the delimiterfield (when included) may act as a cyclic prefix of the first compositesequence in the CEF.

FIG. 19 is a diagram of an example preamble format 710 for a control PHYpacket that utilizes a double-length sequence m. A start frame delimiter(SFD) field may include one or more sequences −m. A CEF is selected sothat the −a sequence in the SFD acts as a cyclic prefix for u. FIG. 20is a diagram of another example preamble format 720 for a control PHYpacket that utilizes a double-length sequence m. A delimiter (SFD) mayinclude one or more sequences −m. A CEF is selected so that the −asequence in the SFD acts as a cyclic prefix for u. As can be seen, the uand v sequences are different in the formats of FIGS. 19 and 20. Aformat for a default packet corresponding to the formats of FIGS. 19 and20 may utilize a plurality of a sequences.

Referring again to FIG. 2, with control PHY preamble formats asdiscussed with reference to FIGS. 19 and 20, the control PHY detector 92may include a correlator configured to cross correlate with the sequencea (an “a correlator”) and a correlator configured to cross correlatewith the sequence b (a “b correlator”), in one embodiment. In thisembodiment, the control PHY detector 92 may utilize the output of the acorrelator and the output of the b correlator to determine when an SFDof a default packet or an SFD of a control PHY packet has been received.In another embodiment, the control PHY detector 92 may include an “acorrelator” and a correlator configured to cross correlate with thesequence m (an “m correlator”). In this embodiment, the control PHYdetector 92 may utilize the output of the a correlator and the output ofthe m correlator to determine when an SFD of a default packet or an SFDof a control PHY packet has been received.

An alternative way for auto-detection is to run 128- and 256-Golaycorrelators in parallel during the carrier sensing period (i.e. runningregular PHY and control PHY carrier sensing in parallel), if the carriersensing by the 256-Golay correlator claims a valid control PHY signal,then it will always over-write the carrier sensing result for theregular PHY (i.e. the result with the 128-Golay correlator output).

FIG. 21 is an example correlator 740 that may be utilized in embodimentsthat utilize Gm in the preamble to signal a control PHY packet, andwhere the a and b sequences have lengths of 128. The correlator 740generates a cross correlation (Xm) of the received signal with thesequence m, and a cross correlation (Xn) of the received signal with thesequence n. The correlator 740 may include a Ga/Gb correlator 744 thatgenerates a cross correlation (Xa) between a received signal and thesequence Ga, and that generates a cross correlation (Xb) between thereceived signal and the sequence Gb. An Xb output is coupled to a delayline 746 that provides a delay of 128 chips. The correlator 740 alsoincludes a subtractor 748 and an adder 750. The subtractor 748 iscoupled to an Xa output of the correlator 744 and to an output of thedelay line 746. The subtractor 748 subtracts a delayed version of Xbfrom Xa to generate Xn. The adder 750 is coupled to the Xa output of thecorrelator 744 and to the output of the delay line 746. The adder 750adds the delayed version of Xb to Xa to generate Xm. In the embodimentof FIG. 20, the Ga/Gb correlator 744 can be used also for detectingcross correlations with the sequences a and b. In other embodiments inwhich the lengths of the a and b sequences are not 128, a differentlength delay line may be utilized.

FIG. 22 is an example correlator 756 that may be utilized in embodimentsthat utilize Gm in the preamble to signal a control PHY packet, andwhere the a and b sequences have lengths of 128. The correlator 756generates a cross correlation (Xu) of the received signal with thesequence u, and a cross correlation (Xv) of the received signal with thesequence v. The correlator 756 may include the Gm/Gn correlator 740. TheXn output is coupled to a delay line 758 that provides a delay of 256chips. An Xm output is coupled to a delay line 760 that provides a delayof 256 chips. The correlator 756 also includes an adder 762 and asubtractor 764. The subtractor 764 is coupled to the Xn output of thecorrelator 740 and to an output of the delay line 760. The subtractor748 subtracts a delayed version of Xm from Xn to generate Xv. The adder762 is coupled to the Xm output of the correlator 740 and to an outputof the delay line 758. The adder 762 adds the delayed version of Xn toXm to generate Xu. In the embodiment of FIG. 20, the Gm/Gn correlator740 can be used also for detecting cross correlations with the sequencesm and n. In other embodiments in which the lengths of the a and b arenot 128, a different length delay line may be utilized.

In other embodiments, the control PHY packet may be signaled by using asequence a′ in the STF, where a′ is neither the same as a nor acomplementary sequence of a. The sequence a′ may have the same length asa or it may be half the length of a. In these embodiments, the CEF maycomprise composite sequences utilizing the complementary sequences a andb. In these embodiments, a delimiter field comprising one or more of thesequence −a′ may optionally be included. Also in these embodiments, acyclic prefix optionally may be included prior to the CEF.

In some embodiments, a control PHY packet may be signaled by thespreading sequence used to spread the PHY header. For example, a defaultpacket may utilize the sequence a to spread data in the PHY header,whereas a control PHY packet may utilize the complementary sequence b tospread data in the PHY header. In these embodiments, a receiver maydetect a control PHY packet by cross correlating with the sequences aand b comparing the energy of the two cross correlations. In onespecific example, the sequences a and b may be Golay sequences of length64. Of course, other length sequences may also be utilized.

In some embodiments, there may be multiple types of control PHY packetsof which a BFT packet is one type. In these embodiments, the control PHYpacket may be signaled by the preamble as discussed above with respectto FIGS. 9A, 9B, 10A, 10B, 11A, 11B, 12A, 12B, 13A, 13B, and 14-20. Inorder to then signal a BFT packet as opposed to the other types ofcontrol PHY packets, other information may be encoded in the preambleand/or the PHY header. For example, the order of u and v in the CEF maybe switched to signal a BFT packet. As another example, the spreadingsequence used to spread the PHY header may be used to signal whether thepacket is a BFT packet. As another example, one or more fields in thePHY header (e.g., the payload length field, a BFT field of a PHY headerof a control PHY packet, etc.) may signal a BFT packet.

FIG. 23 is a block diagram of an example control PHY packet preamblegenerator 800 that may be included in the control PHY packet generator76 (FIG. 2) in embodiments corresponding to FIGS. 9A, 9B, 10A, 10B, 11A,11B, 12A, 127B, 13A, 138B, and 14-20. The control PHY packet preamblegenerator 800 may include a control PHY packet preamble controller 804that includes an STF formatter 808 and a CEF formatter 812, each ofwhich may be implemented using hardware, a processor executing machinereadable instructions, or combinations thereof. Each of the formatters808 and 812 is communicatively coupled to at least a cover codegenerator 816 and a signal generator 820.

The signal generator 820 generally receives cover codes and indicationsof when to generate signals using either a chip sequence a or a chipsequence b from the STF formatter 808, the CEF formatter 812 and thecover code generator 816. The chip sequences a and b are complementarysequences. In some embodiments, the signal generator 820 may include amemory device 824, such as RAM, ROM, or another type of memory, to storethe complementary sequences a and b. In other embodiments, the signalgenerator 820 may include a and b sequence generators. In oneembodiments, the signal generator 820 includes a binary selector 826 toselect one of the two complementary sequences a and b for preamblesignal generation. The two complementary sequences a and b havecorrelation properties suitable for detection at a receiving device. Forexample, the complementary spreading sequences a and b may be selectedso that the sum of corresponding out-of-phase aperiodic autocorrelationcoefficients of the sequences a and b is zero. In some embodiments, thecomplementary sequences a and b have a zero or almost-zero periodiccross-correlation. In another aspect, the sequences a and b may haveaperiodic cross-correlation with a narrow main lobe and low-level sidelobes, or aperiodic auto-correlation with a narrow main lobe andlow-level side lobes. In some of these embodiments, the sequences a andb are complementary Golay sequences. Although various lengths of thesequences a and b may be utilized, each of the sequences a and b, insome of the embodiments, has a length of 128-chips.

The cover code generator 816 may include a memory device 828, such asRAM, ROM, or another type of memory, to store sets of cover codes.Similarly, the cover code generator 816 may include a memory device 832,such as RAM, ROM, or another type of memory, to store u/v sequences. Thecover code generator 816 also may include one or more other memorydevices to store other sequences that span all or parts of the STFfield, all or parts of CEF field, or both the STF field and the CEFfield. In response to commands from the STF formatter 808 and the CEFformatter 812, the cover code generator 816 may generate cover codes fora particular PHY preamble.

From the foregoing, it will be appreciated that the control PHY packetpreamble controller 804 may control the signal generator 820 to generatea control PHY packet preamble using only one pair of sequences a and b.In some embodiments, however, in addition to the sequences a and b, thecontrol PHY preamble controller 804 may also control the signalgenerator 820 to utilize other sequences a′ and b′ to generate a controlPHY preamble.

FIG. 24 is a flow diagram of an example method 850 for generating acontrol PHY packet. The method 850 may be utilized in a wirelesscommunication system in which communication devices exchange informationutilizing data units that conform to a first format that includes a MACheader. The control PHY packet conforms to a second format that isdifferent than the first format. The method 850 may be implemented by atransmitter such as the transmitter 12 of FIG. 2.

At block 854, a first portion of a packet may be generated to indicatethat the packet is a control PHY packet. The first portion of the packetmay include a preamble and may include a portion of the PHY header, andthe first portion of the packet may conform at least in some respects tothe first format. At block 858, a second portion of the packet isgenerated according to the second format. The second portion of thecontrol PHY packet includes control PHY information elements.

FIG. 25 is a flow diagram of an example method 870 for decoding acontrol PHY packet. The method 870 may be utilized in a wirelesscommunication system in which communication devices exchange informationutilizing packets that conform to the first format, wherein the controlPHY packets conform to the second format. The method 850 may beimplemented by a receiver such as the receiver 14 of FIG. 2.

At block 874, a first portion of a received packet is analyzed todetermine if the received packet is a control PHY packet. The firstportion of the received packet may include a preamble and may include abeginning portion of the PHY header. If the received packet isdetermined to be a control PHY packet, control PHY information elementsin a second portion of the control PHY packet may be decoded at block878. The second portion of the control PHY packet conforms to the secondformat.

From the foregoing, it will be noted that a control PHY packet, e.g., aBFT packet, a beacon transmission packet, may include or omit variousfields in the header and in the payload depending on implementation andthe requirements of the control procedure. Thus, a BFT packet mayinclude a BF ID field but a control PHY packet used for beacontransmission may omit this field. With respect to encoding, spreading,and modulating the header and the payload, the components 52-56illustrated in FIG. 2 may be used. Alternatively, the header and thepayload of a control PHY packet may be modulated and spread using anexample modulator 1100 illustrated in FIG. 26. Preferably, modulation ofa control PHY header is the same as the modulation of the correspondingcontrol PHY payload.

The modulator 1100 may include a frame check sequence (FCS) generator1102, a padding bit generator 1104, a scrambler 1106, a forward errorcorrection (FEC) bit generator 1108, a constellation mapper 1110, aspreader 1112, and a block and cyclic prefix generator 1114. If desired,the components 1102, 1104, 1108, and 1114 may be omitted. If included,the FCS generator 1102 applies a CRC code to the header or the payload.Similarly, the optional padding bit generator 1104 need not necessarilyapply padding bits. However, padding bits are unconditionally applied ifthe block and cyclic prefix generator is activated. Further, thescrambler 1106 may use either the seed specified in the PHY header or,alternatively, a predetermined seed stored at the receiver, for example.The FEC bit generator 1108 may apply the same low density parity check(LDPC) code as regular or default packets (see FIG. 3B). Theconstellation mapper 1110 may apply any desired modulation scheme to theencoded bits such as BPSK, QPSK, 16 QAM, differential BPSK (DBPSK),differential QPSK (DQPSK), etc.

If desired, the spreader 1112 may apply the same spreading sequence tothe header and/or the payload as used in spreading the preamble of thecontrol PHY packet. Accordingly, the receiving device 14 (see FIG. 1)may use the same correlator for processing the preamble, the header, and(if available) the payload of a control PHY packet. The spreader 1112 insome embodiments may apply a spreading sequence complementary to thespreading sequence used to spread the STF of the control PHY packet.Thus, if a 128-chip Golay sequence a is applied to the STF of a packet,a 128-chip Golay sequence b complementary to a may be applied to thepayload of the packet. In this manner, a device seeking a control PHYpacket such as a beacon will not mistake the payload of another controlPHY packet for the STF of the control PHY packet being sought.

In some configurations, the spreader 1112 may apply a spreading sequenceof a different length to the header and/or the payload. For example, thepreamble of a control PHY packet may be spread with a spreading factor(i.e., length of the spreading sequence) of 128, and the header andpayload of the same packet may be spread with a spreading factor of 64or 32.

When the spreader 1112 applies spreading sequences of different lengthsto various parts of a control PHY packet, the spreading sequences may beselected so as to permit the use of shared correlator architecture. Tobetter illustrate such efficient shared correlator architecture, anexample correlator 1130 associated with a pair of complementary 128-chipGolay sequences is discussed next with reference to FIG. 27A. As isknown, a pair of complementary Golay sequences may be defined by aweight vector W and a delay vector D. In particular, a pair of 128-chipGolay sequences a₁₂₈ and b₁₂₈ may be defined by

W₁₂₈=[W₁ W₂ W₃ W₄ W₅ W₆ W₇] and   (1)

D₁₂₈=[D₁ D₂ D₃ D₄ D₅ D₆ D₇],   (2)

and implemented in hardware, firmware, or software as a plurality ofmultipliers 1132, delay elements 1134, and adders/subtractors 1136. Inoperation, the correlator 1130 receives an input signal 1140 and outputsa pair of cross-correlation signals Xa and Xb indicative of correlationbetween the input signal 1140 and the sequences a₁₂₈ and b₁₂₈,respectively.

To permit efficient reuse of the architecture of the correlator 1130,the vector D₁₂₈ may be given by

D₁₂₈=[64 D₂ D₃ D₄ D₅ D₆ D₇],   (3)

so that vectors W₆₄ and D₆₄ given by

W₆₄=[W₂ W₃ W₄ W₅ W₆ W₇] and   (4)

D₆₄=[D₂ D₃ D₄ D₅ D₆ D₇]  (5)

define complementary Golay sequences a₆₄ and b₆₄ that are the firsthalves of the respective sequences a₁₂₈ and b₁₂₈. Referring to FIG. 27B,a correlator 1150 implements the algorithm associated with the W₆₄ andD₆₄ to process 64-chip sequences in the header and/or the payload of acontrol PHY packet, while the correlator 1130 of FIG. 27A may process128-chip sequences in the preamble of the same control PHY packet. Itwill be noted that the architecture of the correlators 1130 and 1150 isgenerally the same, except that the correlator 1130 effectively extendsthe correlator 1150 by an additional stage to process another delayelement and another multiplication factor.

As another example, the vector D′₁₂₈ associated with a pair ofcomplementary Golay sequences a′₁₂₈ and b′₁₂₈ may be given by

D′₁₂₈=[D₁ D₂ D₃ D₄ D₅ D₆ 64],   (6)

and the corresponding pair of vectors W′64 and D′64 may be given by

W′₆₄=[W₁ W₂ W₃ W₄ W₅ W₆] and   (7)

D′₆₄=[D₁ D₂ D₃ D₄ D₅ D₆],   (8)

so that complementary Golay sequences a′₆₄ and b′₆₄ are the secondhalves of the respective sequences a′₁₂₈ and b′₁₂₈. FIG. 27C illustratesan example 64-chip correlator 1160 that generates correlation signalscorresponding to the sequences a′₆₄ and b′₆₄.

Generally speaking, a 128-chip correlator advantageously related to acertain 64-chip correlator as illustrated above may be associated withvectors W₁₂₈ and D″₁₂₈ in with D_(i)=64:

D″₁₂₈=[D₁ . . . 64 . . . D₇],   (9)

so that a pair vectors W″₆₄ and D″₆₄ for generating a pair ofcorresponding 64-chip complementary Golay sequences may be derived byremoving the elements W_(i) and D_(i) from the vectors W₁₂₈ and D″₁₂₈.The corresponding 64-chip correlator may be constructed by removing thestage associated with W_(i) and D_(i) from the 128-chip correlatordefined by W₁₂₈ and D″₁₂₈. Further, a 32-chip correlator based on the128-chip correlator defined by W₁₂₈ and D″₁₂₈ can be constructed in asimilar manner by removing two appropriate stages from the 128-chipcorrelator.

In an embodiment, the weight and delay vectors associated with 128-chipsequences a₁₂₈ and b₁₂₈ are given by:

W₁₂₈=[1 1 −1 1 1 1 −1] and   (10)

D₁₂₈=[64 32 16 8 4 1 2].   (11)

The vectors W₁₂₈ and D₁₂₈ produce the pair of 128-chip Golay sequences

a₁₂₈=D8D727D7D8D7D828D8D727D7272827D7;   (12)

b₁₂₈=EBE414E4EBE4EB1BEBE414E4141B14E4,   (13)

Further, the weight and delay vectors associated with 64-chip sequencesa₆₄ and b₆₄ may be given by:

W₆₄=[1 −1 1 1 1 −1] and   (14)

D₆₄=[32 16 8 4 1 2].   (15)

The vectors W₆₄ and D₆₄ produce the pair of 64-chip Golay sequences

a₆₄=D8D727D7D8D7D828;   (16)

b₆₄=EBE414E4EBE4EB1B,   (17)

It will be noted that the sequences a₆₄ and b₆₄ are the first halves ofthe respective sequences a₁₂₈ and b₁₂₈ given by (12) and (13).

Alternatively, the weight and delay vectors associated with 64-chipsequences a′₆₄ and b′₆₄ may be given by:

W′₆₄=[1 −1 1 −1 1 −1] and   (18)

D′₆₄=[32 16 8 4 1 2].   (19)

The vectors W′₆₄ and D′₆₄ produce the pair of 64-chip Golay sequences

a′₆₄=2827D727282728D8;   (20)

b′₆₄=1B14E4141B141BEB,   (21)

If desired, the pairs a₆₄ and b₆₄ and a′₆₄ and b′₆₄ may be used tospread the preamble, header, and data portions of a control PHY packet.Similarly, any of the sequences a₆₄, b₆₄, a′₆₄ or b′₆₄ may be used as“fixed” cyclic prefix sequences used by the block generator 1114.

As another addition or alternative to the architecture illustrated inFIGS. 2 and 26, a modulator and spreader 1170 illustrated in FIG. 28 maymodulate and spread one or several of a control PHY packet preamble,header, and payload using one data bit to select between complementarysequences a and b. The modulator and spreader 1170 includes aconstellation mapper 1172 that maps N-1 bits to a symbol according tothe selected modulating scheme (e.g., BPSK, QPSK, QAM). However, theencoded bits may be grouped into sets of N bits, so that one bit maycontrol the spreader 1174. In particular, the spreader 1174 mayselectively apply one of a pair of complementary sequences a and b toeach constellation symbol generated by the constellation mapper 1172.The spreading sequences a and b may be, for example, complementary Golaysequences of any desired length (e.g., 32, 64, 128), and the length maybe also be selectable to allow transmitting control PHY preambles,headers, and payloads with different spreading factors. In theseembodiments, the spreader 1170 may be implemented as illustrated inFIGS. 27A-C.

Thus, the modulator and spreader 1170 may prepare each set of N bits fortransmission as a certain constellation symbol spread using a certainspreading sequence. Optionally, the modulator and spreader 1170 includesa π/2 rotator to reduce peak-to-power ratio (PAPR). As another option,the modulator and spreader 1170 may omit or bypass the constellationmapper 1172, and directly modulate individual bits by selecting betweencomplementary sequences a and b.

Several additional techniques of modulating and spreading variousportions of a control PHY packet, at least some of which may be used inconjunction with the techniques discussed above, are considered next.Referring again to FIG. 26, a transmitting device in some embodimentsmay include the block and cyclic prefix generator 1114. If desired, thecorresponding receiving device may apply a frequency domain equalizer atthe chip level prior to processing the sequences of chips using adespreader (such as the despreader 88 of FIG. 2, for example). In thismanner, the receiving device may reduce or completely removeinter-symbol interference (ISI) caused by long channel delay spreading.

In some embodiments, 512 chips (e.g., four symbols each spread with thespreading factor of 128) may be aggregated into a single block, and thelast 128 chips of the block may be pre-pended to the block as a cyclicprefix. It will be noted that a similar technique may be used ingenerating the STF and/or CEF fields of a control PHY packet preamble(see, e.g., FIGS. 16-18). It will be further noted that a fast Fouriertransform (FFT) engine of an OFDM device is typically of size 512, andthe block and cyclic prefix generator 1114 may accordingly use the FFTengine to process blocks of 512 chips.

In another embodiment, a known Golay sequence of 64 or 128 chips, forexample, may be added to a block of 448 or 384 chips, respectively, as acyclic prefix. Using known sequences in this manner provides reliablefrequency and channel tracking as the rest of the packet is transmitted.Further, padding may be applied to form an integer number of blocks ineach packet (because the receiving device 14 may not perform frequencydomain equalization with a non-integer number of blocks). If desired, a64-chip or a 128-chip sequence used to spread a portion of the datapacket may also be used to define the cyclic prefix of a block.

Further, it will be noted that when the cyclic prefix generator 1114 isapplied, the padding bit generator 1102 preferably adds padding bitsprior to passing the data bits to the scrambler 1106 to define aninteger number of blocks. Both the receiving device 14 and thetransmitting device 12 can calculate the number of padding bits based onthe length subfield in the header and the modulation method of thecontrol PHY packet.

Next, FIGS. 29A-34B illustrate several example preamble formats for acontrol PHY packet, in which the STF includes spreading sequences thatare neither identical nor complementary to the spreading sequences usedin the formats of FIGS. 8A and 8B. As in the examples discussed above,the formats of FIGS. 29A-34B may be used in control PHY packetsassociated with beamforming or other PHY control procedures.

FIGS. 29A and 29B are diagrams of two example preamble format for acontrol PHY packet. FIGS. 29A and 29B generally correspond to thedefault formats illustrated in FIGS. 8A and 8B, respectively. Inparticular, FIG. 29A is a diagram of the preamble format 1200, whichcorresponds to FIG. 8A. FIG. 29B is a diagram of the preamble format1210, which corresponds to FIG. 8B. In the formats illustrated in FIGS.29A and 29B, the Golay sequence G′a is used to spread at least a portionof the STF.

Compared to the Golay sequence Ga used in the format of FIG. 8A, thesequence G′a is neither identical nor complementary to Ga. Rather, thesequence G′a is unrelated to the sequence Ga. In the format illustratedin FIGS. 29A and 29B, the sequence G′a signals that the packet is acontrol PHY packet. Also in the format illustrated in FIGS. 29A and 29B,a delimiter field 1202 is included after the STF. The delimiter field1202 may be useful for improving frame timing reliability, for example.The delimiter 1202 may include one or more sequences G′a.

Further, the CEF's in FIGS. 29A and 29B are the same as in FIGS. 8A and8B, respectively. Because the sequence G′a is unrelated to the sequencesGa and Gb used in the CEF, the packets 1200 and 1210 include a cyclicprefix field 1204 that corresponds to the last portion of the CEF symbolu or v of the respective CEF.

FIGS. 30A and 30B are diagrams of two example preamble format for acontrol PHY packet. FIGS. 30A and 30B generally correspond to thedefault formats illustrated in FIGS. 8A and 8B, respectively. Thepreamble formats 1220 and 1230, respectively, are similar to thepreamble formats 1200 and 1210, except that the formats 1220 and 1230omit the cyclic prefix field 1204.

FIGS. 31A and 31B are diagrams of two example preamble format for acontrol PHY packet. FIGS. 31A and 31B generally correspond to thedefault formats illustrated in FIGS. 8A and 8B, respectively. Inparticular, FIG. 31A is a diagram of the preamble format 1240, whichcorresponds to FIG. 8A. FIG. 31B is a diagram of the preamble format1250, which corresponds to FIG. 8B. In the formats illustrated in FIGS.31A and 31B, a pair of complementary Golay sequences G′a and G′b areused to spread both the STF and the CEF. Compared to the Golay sequencesGa and Gb used in the format of FIG. 8A, the sequences G′a and G′b areneither identical to Ga or Gb nor complementary of Ga or Gb. Rather,each of the sequences G′a and G′b is unrelated to the sequence Ga or Gb.In the formats illustrated in FIGS. 31A and 31B, the sequence G′a in theSTF signals that the packet is a control PHY packet. Also in the formatsillustrated in FIGS. 31A and 31B, a delimiter field 1242 is includedafter the STF. The delimiter field 1242 may be useful for improvingframe timing reliability, for example. The delimiter field 1242 mayinclude one or more sequences −G′a. Further, a cyclic prefix field 1244includes the sequence G′a which corresponds to the last portion of theCEF symbol u or v of the respective CEF. It will be noted that the signof the sequence G′a in the delimiter field 1242 is flipped relative tothe earlier portion of the STF as well as relative to the cyclic prefixfield 1244.

FIGS. 32A and 32B are diagrams of two example preamble format for acontrol PHY packet. FIGS. 32A and 32B generally correspond to thedefault formats illustrated in FIGS. 8A and 8B, respectively. Thepreamble formats 1260 and 1270 are similar to the preamble formats 1240and 1250, respectively, except that the formats 1260 and 1270 omit thecyclic prefix field 1244.

FIGS. 33A and 33B are diagrams of a preamble format for a control PHYpacket. FIGS. 33A and 33B generally correspond to the default formatsillustrated in FIGS. 8A and 8B, respectively. In particular, FIG. 33A isa diagram of the preamble format 1280, which corresponds to FIG. 8A.FIG. 33B is a diagram of the preamble format 1290, which corresponds toFIG. 8B. In the formats illustrated in FIGS. 33A and 33B, a shorterGolay sequence Ga₆₄ is used to spread a portion of the STF. For example,the sequences a and b used in the formats of FIGS. 8A and 8B may be128-chip Golay sequences Ga₁₂₈ and Gb₁₂₈, whereas the Golay sequenceGa₆₄ is a 64-chip sequence. If desired, the Golay sequence Ga₆₄ may bethe first half or the second half of the sequence Ga₁₂₈, or otherwiserelated to the sequence Ga₁₂₈ (e.g., generated by omitting a stagecorresponding to D_(i)=64 and W_(i) using the techniques discussed withreference to FIGS. 27A-27C). Alternatively, the Golay sequence Ga₆₄ maybe unrelated to the sequences Ga₁₂₈ or Gb₁₂₈.

In the formats illustrated in FIGS. 33A and 33B, the shorter sequenceGa₆₄ in the STF signals that the packet is a control PHY packet. Also inthe formats illustrated in FIGS. 33A and 33B, a delimiter field 1282 isincluded after the STF. The delimiter field 1282 may be useful forimproving frame timing reliability, for example. The delimiter field1282 may include one or more sequences −Ga₆₄. Further, a cyclic prefixfield 1284 includes the longer sequence Ga₁₂₈ which corresponds to thelast portion of the CEF symbol u or v of the respective CEF.

FIGS. 34A and 34B are diagrams of a preamble format for a control PHYpacket. FIGS. 34A and 34B generally correspond to the default formatsillustrated in FIGS. 8A and 8B, respectively. The preamble formats 1300and 1310 are similar to the preamble formats 1280 and 1290,respectively, except that the formats 1300 and 1310 omit the cyclicprefix field 1284.

Generally with respect to control PHY formats discussed above, thereceiving device 14 (see FIG. 1) may further benefit from detecting aparticular type of a control PHY relatively early, i.e., prior toreceiving the entire packet or even the entire header. For example, thereceiving device 14 may determine that a packet is a control PHY packetbased on the STF, and further determine that the control PHY packet is aBFT packet based on the SFD or CEF, for example. In the preamble formats1320 and 1330 illustrated in FIGS. 35A and 35B, the sequence b,complementary to the sequence a used in the default formats of FIGS. 8Aand 8B, is used to spread the STF. Additionally, the SFD in the format1320 includes a 2-length sequence −b, −b to indicate that the packet isa control PHY packet unrelated to beamforming, and the SFD in the format1330 includes a 2-length sequence −b, b to indicate that the packet is aBFT packet. In another example, the second −b sequence in the SFD of theformat 1320 (i.e., the sequence −b adjacent to the CEF) may be replacedwith a (or Ga). In another example, the b sequence in the SFD of theformat 1330 (i.e., the sequence b adjacent to the CEF) may be replacedwith −a (or −Ga). In these examples, the 2-length sequence −b, a in theSFD of the format 1320 indicates that the packet is a control PHY packetunrelated to beamforming, and the SFD in the format 1330 includes a2-length sequence −b, −a to indicate that the packet is a BFT packet.

In general, the formats 1320 and 1330 need not be limited to signalingcontrol PHY packets. It is possible to signal other parameters usingvarious cover codes and/or complementary sequences in the SFD field.Thus, the sequence −b, −b may signal one value of any desired parameter(or formatting option) in the remaining portion of the packet, and thesequence −b, b may signal another value of the parameter. Of course,these sequences may be used in conjunction with other formatting optionsdiscussed herein, as illustrated in FIGS. 35A-B. As one example, theremay be multiple types of control PHY packets having different formats,which may be referred to as sub-formats of the control PHY packet. TheSFD field may be utilized to indicate to which of the sub-formats thecontrol PHY conforms. For instance, one of the sub-formats maycorrespond to a BFT packet, whereas the other sub-formats may correspondto other types of control PHY packets. Thus, the SFD field may indicatewhether the control PHY packet is a BFT packet. As another example, theSFD field may indicate whether the control PHY packet includes apayload.

FIGS. 36A are 36B are diagrams of two example preamble formats forcontrol PHY packets unrelated to beamforming and BFT packets. Inparticular, the STF of each of the formats 1340 and 1350 indicates thatthe packet is a control PHY packet according to one of the techniquesdiscussed above (e.g., using a complementary sequence, sign flipping,etc.). Further, in the format 1340, the ordering of 512-chip sequences uand v indicates that the packet is a control PHY packet unrelated tobeamforming, whereas the opposite ordering of the sequences u and v inthe format 1350 indicates that the packet is a BFT packet.

As illustrated above in FIGS. 13A-B, 14, or 18, the complementarysequence b may be used in the STF to signal that the packet is a controlPHY packet, and an additional delimiter field between the STF and theCEF may be useful for improving frame timing reliability. However, thesequences u and v in the formats of FIGS. 13A-B, 14, and 18 are notidentical to the sequences u and v used in the default formatillustrated in FIGS. 8A-B. Because it may be desirable to use the samecorrelator architecture for “regular” SC/OFDM and control PHY packets,an additional field may be used to permit the use of the same sequencesu and v in the CEF's of all packets. As one example, FIGS. 37A and 37Bare diagrams of two example preamble formats for a control PHY packet.FIG. 37A is a diagram of the preamble format 1360, which corresponds toFIG. 8A, and FIG. 37B is a diagram of the preamble format 1370 f, whichcorresponds to FIG. 8B. In addition to one or several instances of thefield 1362 at the end of the STF, each of the formats 1360 and 1370includes a field 1364 with a spreading sequence complementary to boththe last sequence of the STF field and the first sequence of the CEFfield. It is noted that the CEF's in FIGS. 37A and 37B are the same asin FIGS. 8A and 8B, respectively. If desired, the sign of the sequencein the field 1364 also may be flipped, although the field 1364 accordingto the formats 1360 and 1370 conveniently serves as a cyclic prefix ofthe respective CEF sequence u or v.

As another alternative, illustrated in FIGS. 38A-B are two examplepreamble formats 1380 and 1390, which correspond to FIGS. 8A and 8B,respectively. In the formats 1380 and 1390, the STF may be spread usingthe sequence a, and may include one or several instances of the sequence−a in a field 1382. The field 1382 may indicate that the packet is acontrol PHY packet. To use the same sequences u and v in the CEF as inthe format of FIGS. 8A-B, the format may include a field 1384 with oneor more instances of the sequence a. It is also contemplated that thefields 1364 and 1384 may be omitted in the respective formats of FIGS.37A-38B at a relatively low cost to the resulting reliability andaccuracy.

FIG. 39 is a block diagram of an example transmitting device 1400 and anexample receiving device 1404 similar to the transmitting device 12 andthe receiving device 14 of FIG. 2. The transmitting device 1400 maygenerally convert a sequence of information bits into signalsappropriate for transmission through a wireless channel (e.g., channel16 of FIG. 1), and may have some of the same components as thetransmitting device 12 of FIG. 2. The receiving device 14 may generallyreceive the transmitted signals and attempt to regenerate theinformation bits transmitted by the transmitting device 1400, and mayhave some of the same components as the receiving device 14 of FIG. 2.

The transmitting device 1400 may include a data unit generator 1408configured to choose a delimiter field from a plurality of differentdelimiter fields corresponding to a plurality of different data unitformats or sub-formats. For example, the plurality of differentdelimiter fields may utilize different spread codes and/or differentcover codes. The data unit generator 1408 generates a first portion ofthe data unit that includes a preamble having the chosen delimiterfield, and wherein at least the chosen delimiter field indicates thedata unit conforms to the one format or sub-format. Additionally, thedata unit generator 1408 generates a second portion of the data unitaccording to the one format or sub-format.

The receiving device 1404 may include a data unit format detector 1412configured to detect a delimiter field in a preamble of a received dataunit, and determine one of the plurality of formats based on thedelimiter field. The receiving device 1404 also may include a decoder1416 to decode the received data unit according to the determined oneformat. For example, the data unit format detector 1412 may generate anindication of the detected format and provide the indication to thedecoder 1416. The decoder 1416 may then decode the data unit accordingto the indicated format.

In one embodiment for use in a wireless communication system whereincommunication devices exchange information utilizing data units thatconform to a first format, a method is for generating a physical layer(PHY) data unit that conforms to a second format, wherein the PHY dataunit is for transmitting PHY information. The method may comprisegenerating a preamble of the PHY data unit to indicate the PHY data unitconforms to the second format, and generating a second portion of thePHY data unit according to the second format, wherein the second portionof the PHY data unit includes PHY information elements. Generating thepreamble to indicate the PHY data unit conforms to the second format mayspreading a short training field (STF) of the preamble using a differentspread code than used in the first format. Generating the preamble toindicate the PHY data unit conforms to the second format may comprisespreading a short training field (STF) of the preamble using a differentcover code than used in the first format.

The second format may comprise a plurality of sub-formats, and themethod may further comprise setting at least one field in a PHY headerof the PHY data unit to indicate that the PHY data unit conforms to oneof the sub-formats. For example, a first sub-format may include apayload and a second sub-format may omit the payload, and setting atleast one field in the PHY header of the PHY data unit may includesetting at least one field in the PHY header of the PHY data unit toindicate whether the PHY data unit includes the payload. As anotherexample, one of the sub-formats may correspond to a beamforming training(BFT) data unit, and setting at least one field in the PHY header of thePHY data unit may include setting at least one field in the PHY headerof the PHY data unit to indicate whether the PHY data unit is a BFT dataunit. Additionally, the method may comprise choosing a delimiter fieldfrom a plurality of different delimiter fields corresponding to theplurality of sub-formats, and generating the first portion of the dataunit may include generating the preamble to have the chosen delimiterfield, wherein at least the chosen delimiter field indicates the dataunit conforms to one sub-format from the plurality of sub-formats.

Generating the second portion of the PHY data unit according to thesecond format may comprise generating a PHY header to include PHYinformation elements not specified by the first format. For example, thefirst format may specify a media access control (MAC) header, andgenerating the second portion of the PHY data unit according to thesecond format may comprise generating a fixed-length payload of the PHYdata unit that omits at least some of the MAC header specified by thefirst format.

Generating the second portion of the PHY data unit according to thesecond format may comprise omitting a payload from the PHY data unit.

Generating the second portion of the PHY data unit according to thesecond format may comprise generating the PHY header to conform to thefirst format, and generating a payload that does not conform to thefirst format, wherein the payload includes PHY information elements notspecified by the first format.

The PHY data unit may be a beamforming training (BFT) data unit, and thesecond portion of the BFT data unit includes BFT information elements.

In another embodiment, a communication device for use in a wirelesscommunication system is provided, wherein the communication deviceexchanges information with other communication devices utilizing dataunits that conform to a first format, and utilizes a physical layer(PHY) data unit that conforms to a second format, wherein the PHY dataunit is for transmitting PHY information. The communication device maycomprise a PHY data unit generator configured to generate a preamble ofthe PHY data unit to indicate the PHY data unit conforms to the secondformat, and to generate a second portion of the PHY data unit accordingto the second format, wherein the second portion of the PHY data unitincludes PHY information elements.

The PHY data unit generator may be configured to spread a short trainingfield (STF) of the preamble using a different spread code than used inthe first format, and/or to spread the STF of the preamble using adifferent cover code than used in the first format.

The communication device may further comprise a PHY controller tocontrol the PHY data unit generator during implementation of PHYfunctions.

The communication device may further comprise a modulator to modulatethe PHY data unit.

In another embodiment for use in a wireless communication system whereincommunication devices exchange information utilizing data units thatconform to a first format, a method is for generating a physical layer(PHY) data unit that conforms to a second format, wherein the PHY dataunit is for transmitting PHY information. The method comprises analyzinga preamble of a received data unit to determine if the received dataunit is a PHY data unit. The method also comprises utilizing PHYinformation elements in a second portion of the PHY data unit to performa PHY function if the received data unit is a PHY data unit, wherein thesecond portion of the PHY data unit conforms to the second format, andwherein the PHY information elements are not specified by the firstformat.

Analyzing the preamble of the received data unit is a PHY data unit maycomprise determining if a short training field (STF) of the preamble wasspread using a different spread code than used in the first format,and/or determining if the STF of the preamble was spread using adifferent cover code than used in the first format.

The PHY data unit may be a beamforming training (BFT) data unit, and thesecond portion of the BFT data unit may include BFT informationelements, and utilizing PHY information elements in the second portionof the PHY data unit may comprise performing a beamforming trainingfunction.

The second format may comprise a plurality of sub-formats, and themethod may further comprise analyzing a PHY header of the PHY data unitto determine if the PHY data unit conforms to one of the sub-formats, oranalyzing a frame delimiter of the preamble to determine if the PHY dataunit conforms to one of the sub-formats.

Utilizing PHY information elements in the second portion of the PHY dataunit may comprise utilizing PHY information elements in a PHY header,wherein the PHY information elements in the PHY header are not specifiedby the first format.

The first format may specify a media access control (MAC) header, andwherein the PHY data unit includes a fixed-length payload that omits atleast some of the MAC header specified by the first format.

The PHY data unit may omit a payload.

The PHY data unit may include a PHY header that conforms to the firstformat, and the PHY data unit may includes a payload that does notconform to the first format, wherein the payload includes PHYinformation elements.

In another embodiment, a communication device is for use in a wirelesscommunication system, wherein the communication device exchangesinformation with other communication devices utilizing data units thatconform to a first format, wherein the communication device utilizes aphysical layer (PHY) data unit that conforms to a second format, whereinthe PHY data unit is for transmitting PHY information. The communicationdevice may comprise a PHY data unit detector configured to analyze apreamble of a received data unit to determine whether a short trainingfield (STF) is spread using a different spread code than used in thefirst format and/or to determine whether the STF is spread using adifferent cover code than used in the first format. The communicationdevice also comprises a PHY controller to utilize the PHY informationelements in a second portion of the PHY data unit to perform a PHYfunction if the received data unit is a PHY data unit, wherein thesecond portion of the PHY data unit conforms to the second format, andwherein the PHY information elements are not specified by the firstformat.

The PHY controller may comprise a beamforming training controller.

The communication device may further comprise a demodulator todemodulate the received data unit.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

Although the forgoing text sets forth a detailed description of numerousdifferent embodiments, it should be understood that the scope of thepatent is defined by the words of the claims set forth at the end ofthis patent. The detailed description is to be construed as exemplaryonly and does not describe every possible embodiment because describingevery possible embodiment would be impractical, if not impossible.Numerous alternative embodiments could be implemented, using eithercurrent technology or technology developed after the filing date of thisdisclosure, which would still fall within the scope of the claims.

1. In a wireless communication system wherein communication devicesexchange information utilizing data units that conform to a firstformat, wherein the first format includes a short training field (STF)spread with a first spread code and a first cover code, a method forgenerating a physical layer (PHY) data unit that conforms to a secondformat, wherein the PHY data unit is for transmitting PHY information,the method comprising: generating a first portion of the PHY data unitto indicate the PHY data unit conforms to the second format, wherein thefirst portion of the PHY data unit includes an STF spread with at leastone of a second spread code different than the first spread code or asecond cover code different than the first cover code; and generating asecond portion of the PHY data unit according to the second format,wherein the second portion of the PHY data unit includes PHY informationelements not specified by the first format.
 2. A method according toclaim 1, wherein the second spread code is a complementary sequence ofthe first spread code; wherein the first portion of the PHY data unitincludes the STF spread with the second spread code.
 3. A methodaccording to claim 2, wherein the first spread code and the secondspread code are complimentary Golay sequences a and b, respectively. 4.A method according to claim 3, wherein the STF of the first formatcomprises a plurality of consecutive Golay sequences a; and wherein theSTF of the second format comprises a plurality of consecutive Golaysequences b.
 5. A method according to claim 4, wherein the STF of thesecond format comprises a delimiter field after the plurality ofconsecutive Golay sequences b; and wherein delimiter field includes atleast one Golay sequence −b.
 6. A method according to claim 5, wherein aGolay sequence a is included between the STF of the second format and achannel estimation field (CEF).
 7. A method according to claim 2,wherein the first format includes a channel estimation field (CEF);wherein the first portion of the PHY data unit includes the CEF field ofthe first format.
 8. A method according to claim 7, wherein the STF ofthe PHY data unit includes a delimiter field prior to the CEF field. 9.A method according to claim 8, wherein the STF of the PHY data unitincludes a cyclic prefix for the CEF field after the delimiter field.10. A method according to claim 8, wherein the second format comprisestwo or more sub-formats; wherein the method further comprises generatingthe delimiter field of the PHY data unit to indicate that the PHY dataunit conforms to one of the sub-formats.
 11. A method according to claim10, wherein one of the sub-formats corresponds to a data unit used inbeamforming training.
 12. A communication device for use in a wirelesscommunication system, wherein the communication device exchangesinformation with other communication devices utilizing data units thatconform to a first format, wherein the first format includes a shorttraining field (STF) spread with a first spread code and a first covercode, and utilizing a physical layer (PHY) data unit that conforms to asecond format, wherein the PHY data unit is for transmitting PHYinformation, the communication device comprising: a PHY data unitgenerator configured to: generate a first portion of the PHY data unitto indicate the PHY data unit conforms to the second format, wherein thefirst portion of the PHY data unit includes an STF spread with at leastone of a second spread code different than the first spread code or asecond cover code different than the first cover code, and generate asecond portion of the PHY data unit according to the second format,wherein the second portion of the PHY data unit includes PHY informationelements not specified by the first format.
 13. A communication deviceaccording to claim 12, wherein the second spread code is a complementarysequence of the first spread code; wherein the PHY data unit generatoris configured to generate the STF of the PHY data unit spread with thesecond spread code.
 14. A communication device according to claim 13,wherein the first spread code and the second spread code arecomplimentary Golay sequences a and b, respectively.
 15. A communicationdevice according to claim 14, wherein the STF of the first formatcomprises a plurality of consecutive Golay sequences a; and wherein thePHY data unit generator is configured to generate the STF of the PHYdata unit to include a plurality of consecutive Golay sequences b.
 16. Acommunication device according to claim 15, wherein the PHY data unitgenerator is configured to generate the STF of the PHY data unit toinclude a delimiter field after the plurality of consecutive Golaysequences b; and wherein delimiter field includes at least one Golaysequence −b.
 17. A communication device according to claim 16, whereinthe PHY data unit generator is configured to include a Golay sequence abetween the STF of the second format and a channel estimation field(CEF).
 18. A communication device according to claim 12, furthercomprising a PHY controller to control the PHY data unit generatorduring implementation of PHY functions.
 19. A communication deviceaccording to claim 12, further comprising a modulator to modulate thePHY data unit.
 20. In a wireless communication system whereincommunication devices exchange information utilizing data units thatconform to a first format, wherein the first format includes a shorttraining field (STF) spread with a first spread code and a first covercode, a method for processing a physical layer (PHY) data unit thatconforms to a second format, wherein the PHY data unit is fortransmitting PHY information, the method comprising: analyzing a firstportion of a received data unit to determine if the received data unitis a PHY data unit, wherein the first portion of the received data unitincludes an STF; wherein analyzing the first portion of a received dataunit to determine if the received data unit is a PHY data unit comprisesdetermining at least one of 1) whether the STF of the received data unitis spread with a second spread code different than the first spread codeor 2) whether the STF of the received data unit is spread with a secondcover code different than the first cover code; wherein the methodfurther comprises utilizing PHY information elements in a second portionof the PHY data unit to perform a PHY function if the received data unitis a PHY data unit, wherein the second portion of the PHY data unitconforms to the second format, and wherein the PHY information elementsare not specified by the first format.
 21. A method according to claim20, wherein the second spread code is a complementary sequence of thefirst spread code; and wherein analyzing the first portion of thereceived data unit comprises determining whether the STF of the receiveddata unit is spread with the second spread code.
 22. A method accordingto claim 21, wherein the first spread code and the second spread codeare complimentary Golay sequences a and b, respectively.
 23. A methodaccording to claim 22, wherein the STF of the first format comprises aplurality of consecutive Golay sequences a; and wherein analyzing thefirst portion of the received data unit comprises determining whetherthe STF of the received data unit comprises a plurality of consecutiveGolay sequences b.
 24. A method according to claim 23, wherein the STFof the second format comprises a delimiter field after the plurality ofconsecutive Golay sequences b; wherein delimiter field includes at leastone Golay sequence −b; wherein the method further comprises detectingthe delimiter field.
 25. A method according to claim 24, wherein a Golaysequence a is included between the STF of the second format and achannel estimation field (CEF).
 26. A method according to claim 20,wherein the PHY data unit is a beamforming training (BFT) data unit;wherein the second portion of the BFT data unit includes BFT informationelements not specified by the first format; wherein utilizing PHYinformation elements in the second portion of the PHY data unitcomprises performing a beamforming training function.
 27. Acommunication device for use in a wireless communication system, whereinthe communication device exchanges information with other communicationdevices utilizing data units that conform to a first format, wherein thefirst format includes a short training field (STF) spread with a firstspread code and a first cover code, and utilizing a physical layer (PHY)data unit that conforms to a second format, wherein the PHY data unit isfor transmitting PHY information, the communication device comprising: aPHY data unit detector configured to: analyzing a first portion of areceived data unit to determine if the received data unit is a PHY dataunit, wherein the first portion of the received data unit includes anSTF; determine if the received data unit is a PHY data unit based ondetermining at least one of 1) whether the STF of the received data unitis spread with a second spread code different than the first spread codeor 2) whether the STF of the received data unit is spread with a secondcover code different than the first cover code; wherein thecommunication device further comprises a PHY controller to utilize thePHY information elements in a second portion of the PHY data unit toperform a PHY function if the received data unit is a PHY data unit;wherein the second portion of the PHY data unit conforms to the secondformat; and wherein the PHY information elements are not specified bythe first format.
 28. A communication device according to claim 27,wherein the second spread code is a complementary sequence of the firstspread code; wherein the PHY data unit detector configured to determinewhether the STF of the received data unit is spread with the secondspread code.
 29. A communication device according to claim 28, whereinthe first spread code and the second spread code are complimentary Golaysequences a and b, respectively.
 30. A communication device according toclaim 29, wherein the STF of the first format comprises a plurality ofconsecutive Golay sequences a; and wherein the PHY data unit detectorconfigured to determine whether the STF of the received data unitcomprises a plurality of consecutive Golay sequences b.
 31. Acommunication device according to claim 30, wherein the STF of thesecond format comprises a delimiter field after the plurality ofconsecutive Golay sequences b; wherein delimiter field includes at leastone Golay sequence −b; wherein the PHY data unit detector configured todetect the delimiter field.
 32. A communication device according toclaim 27, further comprising a demodulator to demodulate the PHY dataunit.
 33. A communication device according to claim 27, furthercomprising a despreader.